Image displaying panel and image display unit

ABSTRACT

In an image display panel: in which at least one group of particles or liquid particles is sealed between opposed substrates, at least one of two substrates being transparent; in which the particles or the liquid powders, to which an electrostatic field is applied, are made to move so as to display an image; and in which partition walls arranged between the substrates according to need, use is made of the substrate in which at least a surface, to which the particles or the liquid powders are contacted, is subjected to a hydrophobic treatment (first aspect), at least a surface of the partition wall, to which the particles or the liquid powders are contacted, is subjected to a hydrophobic treatment (second aspect), at least a surface of the partition wall, to which the particles or the liquid powders are contacted, is coated by a material having a small charge decay property (third aspect), a universal hardness of a binder resin used for a material constituting the partition wall is not less than 400 N/mm 2 , which is obtained by a method of measuring a universal hardness in which the binder resin constituting the partition wall having a thickness of 3 μm is formed on a glass substrate having a universal hardness of 2000 N/mm 2  (fourth aspect), a ratio Lh/Lw between a height Lh and a width Lw of the partition wall satisfies 0.5≦Lh/Lw≦20 (fifth aspect), and the partition wall has a predetermined drying function (sixth aspect).

TECHNICAL FIELD

The present invention relates to an image display panel, andparticularly relates to an image display device and an image displaypanel used for a reversible image display device enables to repeatedlydisplay images accompanied by flight and movement of particles utilizingCoulomb's force and so on.

BACKGROUND ART

As an image display device substitutable for liquid crystal display(LCD), image display devices with the use of technology such as anelectrophoresis method, an electro-chromic method, a thermal method,dichroic-particles-rotary method are proposed.

As for these image display device, it is conceivable as inexpensivevisual display device of the next generation from a merit having widefield of vision close to normal printed matter, having smallerconsumption with LCD, spreading out to a display for portable device,and an electronic paper is expected. Recently, electrophoresis method isproposed that microencapsulate dispersion liquid made up with dispersionparticles and coloration solution and dispose the liquid between facedsubstrates.

However, in the electrophoresis method, there is a problem that aresponse rate is slow by the reason of viscosity resistance because theparticles migrate among the electrophoresis solution. Further, there isa problem of lacking imaging repetition stability, because particleswith high specific gravity of titanium oxide is scattered withinsolution of low specific gravity, it is easy to subside, difficult tomaintain a stability of dispersion state. Even in the case ofmicroencapsulating, cell size is diminished to a microcapsule level inorder to make it hard to appear, however, an essential problem was notovercome at all.

Besides the electrophoresis method using behavior in the solution,recently, a method wherein electro-conductive particles and a chargetransport layer are installed in a part of the substrate without usingsolution is proposed. [The Imaging Society of Japan “Japan Hardcopy '99”(Jul. 21-23, 1999) Transaction Pages 249-252] However, the structurebecomes complicated because the charge transport layer and further acharge generation layer are to be arranged. In addition, it is difficultto constantly dissipate charges from the electro-conductive particles,and thus there is a drawback on the lack of stability.

However, in the case such that a surface of a substrate, to whichparticles or liquid powders to be sealed having an excellent mobilityare contacted, has such a state that a material constituting thesubstrate is exposed as it is, a durability for a repetition use isinsufficient when it is used as the image display panel. That is, evenin the particles and the liquid powders, there occurs a phenomenonduring the repetition use such that the particles or the liquid powdersare adhered to the surface of the substrate and don't move, and there isa problem such that a contrast of the image is deteriorated (task to besolved by a first aspect of the invention).

Moreover, in the case such that a surface of a substrate or a partitionwall, to which particles or liquid powders to be sealed having anexcellent mobility are contacted, has such a state that a materialconstituting the substrate or the partition wall is exposed as it is, adurability for a repetition use is insufficient when it is used as theimage display panel. That is, even in the particles and the liquidpowders, there occurs a phenomenon during the repetition use such thatthe particles or the liquid powders are adhered to the surface of thesubstrate or the partition wall and don't move, and there is a problemsuch that a contrast of the image is deteriorated. As a result, it isinsufficient on the durability for the repetition use (task to be solvedby a second to a fourth aspects of the invention).

In order to solve the problems mentioned above, it is known an imagedisplay device which comprises an image display panel, in which one ormore groups of particles are sealed in a plurality of cells formed bypartition walls between two substrates, at least one of two substratesbeing transparent, and, in which the particles, to which anelectrostatic field produced by electrodes provided to both of thesubstrate is applied, are made to fly and move so as to display an imageby utilizing Coulomb's force.

In the image display device mentioned above, an opening rate of the cellis varied due to a shape of the partition wall, for example, when thepartition wall is formed on a glass substrate by means of a photo-resistand a plurality of cells are constructed between two substrates.Therefore, in the case such that a ratio between a height Lh and a widthLw of the partition wall is set at a value out of an adequate range,there occurs a decrease of the opening rate and a deterioration of amanufacturing property. This problem occurs in the same manner even inan image display device which comprises an image display panel in whichliquid powders composed of a solid material stably floating as adispersoid in a gas and exhibiting a high fluidity in an aerosol stateor particles are sealed in a plurality of cells formed by partitionwalls between opposed substrates, at least one substrate beingtransparent, and, in which the liquid powders or the particles, to whichan electrostatic field is applied from two kinds of electrodes havingdifferent potentials, are made to fly and move so as to display an image(task to be solved by a fifth aspect of the invention).

Moreover, in the image display device mentioned above, it is possible tocontrol a humidity in the device preferably without using a dryingagent, for example, by adding a drying function to the partition wall.However, when the partition wall is made of a material having a waterabsorption property in order to achieve the drying function mentionedabove, it is important to control a water absorption rate of thepartition wall. In the case such that a water absorption rate of thepartition wall is set at a value out of an adequate range, there occursa case such that a water absorption effect becomes insufficient or wateris excessively absorbed during a device assembly process, so that adisplay property is affected. This problem occurs in the same mannereven in an image display device which comprises an image display panelin which liquid powders composed of a solid material stably floating asa dispersoid in a gas and exhibiting a high fluidity in an aerosol stateor particles are sealed in a plurality of cells formed by partitionwalls between opposed substrates, at least one substrate beingtransparent, and, in which the liquid powders or the particles, to whichan electrostatic field is applied from two kinds of electrodes havingdifferent potentials, are made to fly and move so as to display an image(task to be solved by a sixth aspect of the invention).

DISCLOSURE OF INVENTION

Objects of the first to the fourth aspects of the invention are toeliminate the drawbacks mentioned above and to provide an image displaypanel and an image display device, which are inexpensive and haveexcellent repetition durability even in the case of using the particleshaving an excellent mobility and in the case of using the liquidpowders.

Moreover, an object of the fifth aspect of the invention is to eliminatethe drawback mentioned above and to provide an image display device, inwhich both of the opening rate and the manufacturing property can beassured by designing a shape of the partition wall in such a manner thata ratio between the height Lh and the width Lw of the partition wall isin an adequate range.

Further, an object of the sixth aspect of the invention is to eliminatethe drawback mentioned above and to provide an image display device, inwhich an atmosphere in the device can be made to be even without using adrying agent by adding a predetermined drying function to the partitionwall.

According to the first aspect of the invention, an image display panel:in which at least one group of particles or liquid particles is sealedbetween opposed substrates, at least one of two substrates beingtransparent; and in which the particles or the liquid powders, to whichan electrostatic field is applied, are made to move so as to display animage; is characterized in that use is made of the substrate in which atleast a surface, to which the particles or the liquid powders arecontacted, is subjected to a hydrophobic treatment.

As preferred embodiments of the image display panel according to thefirst aspect of the invention, there are cases: such that as thesubstrate in which the surface, to which the particles or the liquidpowders are contacted, is subjected to the hydrophobic treatment, use ismade of a substrate in which a surface is subjected to ahexamethyldisilazan treatment; such that prior to thehexamethyldisilazan treatment, OH group adding process is performed;such that a water absorption rate of the particles or the liquid powderssealed between the substrates, which is measured according to ASTM D570at 23° C. for 24 hours, is not greater than 3%; and such that a volumeoccupying rate of the particles or the liquid powders sealed between thesubstrates is in a range of 3-70 vol %.

In the image display panel according to the first aspect of theinvention, since at least the surface of the substrate, to which theparticles or the liquid powders are contacted, is subjected to thehydrophobic treatment, the particles and the liquid powders aredifficult to agglutinate and adhere with respect to the surface of thesubstrate, and thus a surface state, wherein the particles and theliquid powders are easily moved, can be achieved. As a result, it ispossible to obtain the image display panel and the image display device,which are inexpensive and have excellent repetition durability.

According to the second aspect of the invention, an image display panel:in which one or more than two cells surrounded by partition walls areformed between opposed two substrates with a predetermined distance, atleast one of two substrates being transparent; in which particles orliquid powders are accommodated in respective cells; and in which theparticles or the liquid powders, to which an electrostatic field isapplied, are made to move so as to display an image; is characterized inthat at least a surface of the partition wall, to which the particles orthe liquid powders are contacted, is subjected to a hydrophobictreatment.

In the image display panel according to the second aspect of theinvention, since at least the surface of the partition wall, to whichthe particles or the liquid powders are contacted, is subjected to thehydrophobic treatment, the particles and the liquid powders aredifficult to agglutinate and adhere with respect to the surface of thepartition wall, and thus a surface state, wherein the particles and theliquid powders are easily moved, can be achieved. As a result, it ispossible to obtain the image display panel and the image display device,which are inexpensive and have excellent repetition durability.

As preferred embodiments of the image display panel according to thesecond aspect of the invention, there are cases: such that the surfaceof the partition wall, to which the particles or the liquid powders arecontacted, is subjected to the hydrophobic treatment usinghexamethyldisilazan; and such that prior to the hydrophobic treatmentusing hexamethyldisilazan, OH group adding process is performed. In bothcases, it is possible to perform the present invention effectively.

According to the third aspect of the invention, an image display panel:in which one or more than two cells surrounded by partition walls areformed between opposed two substrates with a predetermined distance, atleast one of two substrates being transparent, to which an electrostaticfield is applied, are made to move so as to display an image; ischaracterized in that at least a surface of the partition wall, to whichthe particles or the liquid powders are contacted, is coated by amaterial having a small charge decay property.

In the image display panel according to the third aspect of theinvention, since at least the surface of the partition wall, to whichthe particles or the liquid powders are contacted, is coated by amaterial having a small charge decay property, the particles and theliquid powders are difficult to agglutinate and adhere with respect tothe surface of the partition wall, and thus a surface state, wherein theparticles and the liquid powders are easily moved, can be achieved. As aresult, it is possible to obtain the image display panel and the imagedisplay device, which are inexpensive and have excellent repetitiondurability.

As preferred embodiments of the image display panel according to thethird aspect of the invention, there are cases: such that the materialhaving a small charge decay property is a resin including fluorocarbonresin, and, as the fluorocarbon resin, use is made of one or more thantwo kinds of tetrafluoroethylene-perfluoroalkylvinylether copolymer,tetrafluoroethlen-heaxafluoropropylene-perfluoraclkylvinylethercopolymer, tetrofluoroethylene-ethylene copolymer,polychlorotrifluoroethylene, chlorotrifluoroethylene-ethylene copolymer,polytetrafluoroethylene, polyfluoride and polyvinylfluoride; and suchthat the material having a small charge decay property coated to asurface of the partition wall has such a property measured by a chargedecay property measuring method using a coating material as a film thatthe maximum surface potential, in the case that the surface thereof ischarged by a generation of Corona discharge caused by applying a voltageof 8 KV to a Corona discharge device deployed at a distance of 1 mm fromthe surface, is 300 V or greater at 0.3 second after the Coronadischarge. In both cases, it is possible to perform the presentinvention effectively.

According to the fourth aspect of the invention, an image display panel:in which one or more than two cells surrounded by partition walls areformed between opposed two substrates with a predetermined distance, atleast one of two substrates being transparent; in which particles orliquid powders are accommodated in respective cells; and in which theparticles or the liquid powders, to which an electrostatic field isapplied, are made to move so as to display an image; is characterized inthat a universal hardness of a binder resin used for a materialconstituting the partition wall is not less than 400 N/mm², which isobtained by a method of measuring a universal hardness in which thebinder resin constituting the partition wall having a thickness of 3 μmis formed on a glass substrate having a universal hardness of 2000N/mm².

In the image display panel according to the fourth aspect of theinvention, since the universal hardness of the binder resin used for amaterial constituting the partition wall is not less than 400 N/mm²,which is obtained by a method of measuring a universal hardness in whichthe binder resin constituting the partition wall having a thickness of 3μm is formed on a glass substrate having a universal hardness of 2000N/mm², the particles and the liquid powders are difficult to agglutinateand adhere with respect to the surface of the partition wall, and thus asurface state, wherein the particles and the liquid powders are easilymoved, can be achieved. As a result, it is possible to obtain the imagedisplay panel and the image display device, which are inexpensive andhave excellent repetition durability.

As common preferred embodiments of the image display panel according tothe second to the fourth aspects of the invention, there are cases: suchthat a water absorption rate of the particles or the liquid powderssealed between the substrate, which is measured according to ASTM D570at 23° C. for 24 hours, is not greater than 3%; such that a volumeoccupying rate of the particles or the liquid powders sealed between thesubstrates is in a range of 3-70 vol %; and such that the particles orthe liquid powders to be accommodated in the cell having differentcolors and different charge characteristics and having different chargepotentials, and the particles or the liquid powders, to which anelectrostatic field is applied, are made to move so as to display animage.

According to the fifth aspect of the invention, an image display panel:in which at least one group of particles or liquid powders is sealedrespectively in a plurality of cells formed by partition walls betweentwo substrates, at least one of two substrates being transparent; and inwhich the particles or the liquid powders, to which an electrostaticfield is applied, are made to move so as to display an image; ischaracterized in that a ratio Lh/Lw between a height Lh and a width Lwof the partition wall satisfies 0.5≦Lh/Lw≦20.

In the image display panel according to the fifth aspect of theinvention, since the ratio Lh/Lw between a height Lh and a width Lw ofthe partition wall satisfies 0.5≦Lh/Lw≦20, it is possible to eliminatethe shape of the partition wall in which a minimum opening rate requiredin an actual use can not be obtained and also eliminate the shape of thepartition wall which is difficult to manufacture the partition wall, asis clearly understood from the examples explained below. As a result, itis possible to provide the image display panel, which can maintain bothof the opening rate and the manufacturing property.

As a preferred embodiment of the image display panel according to thefifth aspect of the invention, there is a case such that the ratio Lh/Lwbetween the height Lh and the width Lw satisfies 1≦Lh/Lw≦10. In thiscase, it is possible to provide the image display panel, which has anexcellent opening rate and an excellent manufacturing property, as isclearly understood from the examples mentioned below.

According to the sixth aspect of the invention, an image display panel:in which at least one group of particles or liquid powders is sealedrespectively in a plurality of cells formed by partition walls betweentwo substrates, at least one of two substrates being transparent; and inwhich the particles or the liquid powders, to which an electrostaticfield is applied, are made to move so as to display an image; ischaracterized in that the partition wall has a predetermined dryingfunction.

In the image display panel according to the sixth aspect of theinvention, since the partition wall has a predetermined drying function,it is possible to control humidity by using the drying function withoutfilling a drying agent in the device. Therefore, it is possible toprovide the image display panel in which an atmosphere in the device canbe made even without using the drying agent.

As a preferred embodiment of the image display panel according to thesixth aspect of the invention, there is a case such that a waterabsorption rate S of the partition wall satisfies 0.1%≦S≦10%. In thiscase, as is clearly understood from the examples mentioned below, it ispossible to eliminate the case in which a water absorption effectbecomes insufficient and also eliminate the case in which water isexcessively absorbed during a device assembly process and a displayproperty is affected, so that the partition wall achieves apredetermined drying function.

Moreover, according to the invention, an image display device ischaracterized in that the image display panel set forth in the aboveembodiments.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing one embodiment of the display methodusing the particles in the image display panel according to theinvention.

FIG. 2 is a schematic view illustrating another embodiment of thedisplay method using the particles in the image display panel accordingto the invention.

FIG. 3 is a schematic view depicting one embodiment of the panelconstruction using the particles in the image display panel according tothe invention.

FIG. 4 is a schematic view showing one embodiment of the display methodusing the liquid powders in the image display panel according to theinvention.

FIG. 5 is a schematic view illustrating another embodiment of thedisplay method using the liquid powders in the image display panelaccording to the invention.

FIG. 6 is a schematic view depicting one embodiment of the panelconstruction using the liquid powders in the image display panelaccording to the invention.

FIG. 7 is a schematic view showing one embodiment of the apparatus formeasuring the surface potential.

FIG. 8 is schematic view explaining the features on a cross sectionalshape of the partition wall in the image display panel according to thefifth aspect of the invention.

FIGS. 9 a and 9 b are a cross sectional view and a plan viewrespectively illustrating the partition wall in the image display panelaccording to the sixth aspect of the invention.

FIG. 10 is a schematic view depicting one embodiment of the display cellformed by the partition walls.

BEST MODE FOR CARRYING OUT THE INVENTION

In the image display panel according to the first to the sixth aspectsof the invention, wherein the particles or the liquid powders are sealedbetween opposed substrates, an electrostatic field is applied to theparticles or the liquid powders by some kind of means. The particles orthe liquid powders charged in a low potential are attracted toward ahigh potential side by means of Coulomb's force and so on, and theparticles or the liquid powders are attracted toward a low potentialside by means of Coulomb's force and so on. If a direction of theelectrostatic field is varied in response to a switching of potentials,the particles or the liquid powders mentioned above perform areciprocating motion, and thus the image is displayed. Therefore, it isnecessary to design the image display panel so as to move the particlesor the liquid powders evenly and to maintain a stability when arepetition of the image display is performed or when the image is saved.

The image display panel according to the first to the sixth aspects ofthe invention can be applied to both of panel having a display type inwhich two or more groups of particles 3A having different colors(referred to FIG. 1) are moved in a direction perpendicular tosubstrates 1, 2 and a panel having a display type in which one group ofparticles 3A having a color (referred to FIG. 2) or liquid powders 3Bhaving a color (referred to FIG. 5) are moved in a direction parallel tothe substrates 1, 2. One embodiment of a panel construction for thedisplay is shown in FIG. 3 (using the particles 3A) and FIG. 6 (usingthe liquid powders 3B). It should be noted that, in FIGS. 1 to 6, anumeral 4 is a partition wall arranged according to need, and numerals5, 6 are electrodes arranged according to need so as to apply anelectrostatic field to the particles 3A and the liquid powders 3B.

Hereinafter, features of the first to the sixth aspects of the inventionwill be explained respectively. Then, common members of the imagedisplay panel will be explained. After that, examples of respectiveaspects of the invention will be explained.

(As to Features of the First Aspect of the Invention)

A feature of the first aspect of the invention is that, in the imagedisplay panel having the construction mentioned above, a hydrophobictreatment using preferably hexamethyldisilazan is performed with respectto a surface of the substrate 1 opposed to the substrate 2 and/or asurface of the substrate 2 opposed to the substrate 1.

In the first aspect of the invention, it is possible to improvedurability during a repetition use: by making at least a surface of thesubstrate, to which the particles or the liquid powders are contacted,in a hydrophobic state; by making a water content of a materialconstituting the particles or the liquid powders in an adequate range;and by making a filling amount of the particles or the liquid powders inan adequate range.

As a preferred embodiment of a method for making the surface of thesubstrate in a hydrophobic state, the hexamethyldisilazan treatment isperformed with respect to the surface of the substrate. If the surfaceof the substrate is treated by hexamethyldisilazan so as to make it tothe hydrophobic state, the particles and the liquid powders aredifficult to agglutinate and adhere with respect to the surface of thesubstrate, and thus a surface state, wherein the particles and theliquid powders are easily moved, can be achieved. In this case, it ispreferred that, since the surface of the substrate becomes in thehydrophobic state by chemically coupling a functional group existing onthe surface of the substrate and hexamethyldisilazan as shown in thefollowing formula, an affection to the particles or the liquid powdersis minimized.2ROH+Me₃SiNHSiMe₃→2ROSiMe₃+NH₃

As the treatment method, use is made of a wet process wherein: thesubstrate is immersed in a solution of hexamethyldisilazan;hexamethyldisilazan is decomposed by using a centrifugation and so on;and the substrate is heated and dried, and a dry process wherein:hexamethyldisilazan or its solution is introduced on a dried substrateby means of dropping, spraying and so on; and the substrate is heatedand dried. An amount of hexamethyldisilazan to be treated with respectto the surface of the substrate is not particularly limited in thepresent invention, and normally it is sufficient to use a solution inwhich 0.1-10 weight % of hexamethyldisilazan is included. Moreover, as aprior process of the hexamethyldisilazan treatment, it is preferred toperform OH group adding process. This OH group adding process can beperformed by a method such as plasma treatment, NaOH treatment and soon.

As another method for making the surface of the substrate in thehydrophobic state, use is made of a method using another silane couplingagent. Also in this case, the same treatment method as that ofhexamethyldisilazan can be utilized. As such another silane couplingagent, use is made of methyltrichlorosilane, dimethyldichlorosilane,trimethylchlorosilane, methyltrimethoxysilane, dimethyldimethoxysilane,methyltriethoxysilane, dimethyldiethoxysilane, isobutyltrimethoxysilane,decyltrimethoxysilane, ter-butyldimethylchlorosilane,vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane and soon.

(As to Features of the Second to the Fourth Aspects of the Invention)

The present invention is achieved by investigating the partition wall 4formed on the substrate, and has features: such that the particles andthe liquid powders becomes difficult to agglutinate and adhere withrespect to the surface of the partition wall by making the surface ofthe partition wall (rib) in the hydrophobic state and a durability asthe image display panel is improved (second aspect of the invention);such that the particles and the liquid powders becomes difficult toagglutinate and adhere with respect to the surface of the partition wallby coating the surface of the partition wall (rib) with a materialhaving a small charge decay property and a durability as the imagedisplay panel is improved (third aspect of the invention); and such thatthe particles and the liquid powders becomes difficult to agglutinateand adhere with respect to the surface of the partition wall by making auniversal hardness of the binder resin used for a material constitutingthe partition wall (rib) to not less than 400 N/mm² and a durability asthe image display panel is improved (fourth aspect of the invention).

As a preferred embodiment of a method for making the surface of thepartition wall in a hydrophobic state, the hexamethyldisilazan treatmentis performed with respect to the surface of the partition wall. If thesurface of the partition wall is treated by hexamethyldisilazan so as tomake it to the hydrophobic state, the particles and the liquid powdersare difficult to agglutinate and adhere with respect to the surface ofthe substrate, and thus a surface state, wherein the particles and theliquid powders are easily moved, can be achieved. In this case, it ispreferred that, since the surface of the partition wall becomes in thehydrophobic state by chemically coupling a functional group existing onthe surface of the substrate and hexamethyldisilazan as shown in thefollowing formula, an affection to the particles or the liquid powdersis minimized.2ROH+Me₃SiNHSiMe₃→2ROSiMe₃+NH₃

As the treatment method, use is made of a wet process wherein: thesubstrate with the partition wall is immersed in a solution ofhexamethyldisilazan; hexamethyldisilazan is decomposed by using acentrifugation and so on; and the substrate with the partition wall isheated and dried, and a dry process wherein: hexamethyldisilazan or itssolution is introduced on a dried partition wall by means of dropping,spraying and so on; and the partition wall is heated and dried. Anamount of hexamethyldisilazan to be treated with respect to the surfaceof the partition wall is not particularly limited in the presentinvention, and normally it is sufficient to use a solution in which0.1-10 weight % of hexamethyldisilazan is included. Moreover, as a priorprocess of the hexamethyldisilazan treatment, it is preferred to performOH group adding process. This OH group adding process can be performedby a method such as plasma treatment, NaOH treatment and so on.

As another method for making the surface of the partition wall in thehydrophobic state, use is made of a method using another silane couplingagent. Also in this case, the same treatment method as that ofhexamethyldisilazan can be utilized. As such another silane couplingagent, use is made of methyltrichlorosilane, dimethyldichlorosilane,trimethylchlorosilane, methyltrimethoxysilane, dimethyldimethoxysilane,methyltriethoxysilane, dimethyldiethoxysilane, isobutyltrimethoxysilane,decyltrimethoxysilane, ter-butyldimethylchlorosilane,vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane and soon.

Then, in the image display panel according to the third aspect of theinvention, the material having a small charge decay property, which isused for coating the surface of the partition wall, will be explained.

As the material having a small charge decay property, it is specificallyimportant to select a material satisfying the measuring method mentionedbelow. That is, the material used for coating the surface of thepartition wall is made to a film shape having a thickness in a range of5-100 μm, and a Corona discharge is generated by applying a voltage of 8KV to a Corona discharger provided at a position having a distance of 1mm from a surface of the film so as to charge the surface, so that avariation of a surface potential is measured and is determined. In thiscase, it is important to used the material for coating in which amaximum value of the surface potential is 300 V or greater preferably400 V or greater at 0.3 second after the Corona discharge.

As the coating material having a small charge decay property, use ismade of a resin material including fluorocarbon resin. As thefluorocarbon resin, use is made of one or more than two kinds offluorocarbon resins selected from a group oftetrafluoroethlene-perfluoroalkylvinylester copolymer,tetrafluoroethylene-hexafluoropropylene-perfluoroalkylvinylestercopolymer, tetrafluoroethylene-ethylene copolymer,polychlorotrifluoroethylene, chlorotrifluoroethylene-ethylene copolymer,polytetrafluoroethylene, polyfluoride and polycinylfluoride.

As a material having a small charge decay property for coating thepartition wall, it is preferred to blend another resins withfluorocarbon resins mentioned above. In this case, it is preferred thatan amount of fluorocarbon resins is at least not less that 60 weight %preferably not less than 80 weight %.

In this case, the foregoing surface potential is measured by means of anapparatus (CRT2000 produced by QEA Inc.) disclosed in a specificationand drawings of U.S. Pat. No. 22,003. FIG. 7 is a schematic view showingone embodiment of the apparatus for measuring the surface potential. Inthe apparatus shown in FIG. 7, shaft portions 12 of a roll member 11, onwhich a coating resin is arranged, are supported by chucks 13, and, ameasurement unit 16, in which a compact scorotoron discharger 14 and asurface potential meter 15 are provided with a distance of 1 mm from asurface of the roll member 11.

When the measurement is performed, the measurement unit 16 is moved fromone end to the other end of the roll member 11 along a rail 17 with auniform speed, while the roll member 11 remains stationary, and itssurface potential is measured while charging a surface of the rollmember 11. Moreover, a measurement environment should be settled at atemperature of 25±3° C. and a humidity of 55±5%.

A thickness of the coating material is preferably 0.01-100 μm morepreferably 0.1-30 μm. Moreover, as a coating method, use is made ofprinting method, dipping method, electrostatic coating method,sputtering method and so on, but it is not limited. Further, thesubstrate may be coated together with the partition wall.

As for a solvent insoluble rate of the resin material used for coating,it is preferred that a solvent insoluble rate of the resin, which isdefined by the following formula, is not less than 50% more preferablynot less than 70%:solvent insoluble rate (%)=(B/A)×100;(here, A is a weight of the resin before being immersed into the solventand B is a weight of the resin components after the resin is immersedinto good solvent at 25° C. for 24 hours).

If the solvent insoluble rate is less than 50%, a bleed is generated ona surface of the partition wall when maintaining for a long time. Inthis case, it affects an adhesion power with the particles or the liquidpowders and prevents a movement of the particles or the liquid powders.Therefore, there is a case such that it affects a durability of theimage display. Here, as a solvent for measuring the solvent insolublerate, it is preferred to use fluorocarbon resin such asmethylethylketone and so on, polyamide resin such as methanol and so on,acrylic urethane resin such as methylethylketone, toluene and so on,melamine resin such as acetone, isopropanol and so on, and, siliconeresin such as toluene and so on.

(As to a Feature of the Fifth Aspect of the Invention)

Then, a shape of the partition wall 4, which is the feature of the imagedisplay device according to the fifth aspect of the invention, will beexplained with reference to FIG. 8. FIG. 8 is a schematic viewexplaining the features on a cross sectional shape of the partition wallin the image display panel according to the fifth aspect of theinvention. In FIG. 8, when it is assumed that a height of the partitionwall 4 formed on the substrate 1 or 2 is Lh and a width of the partitionwall 4 is Lw, a ratio Lh/Lw is set at a value within an adequate rangeshown in the following formula (1) and is preferably set at a valuewithin an adequate range shown in the following formula (2):0.5≦Lh/Lw≦20  (1)1≦Lh/Lw≦10  (2)

In this embodiment, since the ratio Lh/Lw between the height and thewidth of the partition wall 4 is set in the adequate range shown in theformula (1), it is possible to provide the image display panel, whichhas an excellent opening rate and an excellent manufacturing property.

(As to a Feature of the Sixth Aspect of the Invention)

Then, the partition wall 4, which is the feature of the image displaydevice according to the sixth aspect of the invention, will be explainedwith reference to FIGS. 9 a and 9 b. FIGS. 9 a and 9 b are a crosssectional view and a plan view respectively showing the partition wallin the image display panel according to the sixth aspect of theinvention. On the substrate 1 or 2 shown in FIG. 9 a, a plurality ofpartition walls 4 are formed. Theses plural partition walls 4 have asquare shape with a grid arrangement as shown in FIG. 9 b or havevarious shapes with a honeycomb arrangement as shown in FIG. 10. In thepresent invention, as the partition wall 5, use is made of the partitionwall having a predetermined drying function. Specifically, use is madeof the partition wall 4 having a water absorption rate S within anadequate range shown in the following formula (3):0.1%≦S≦10%  (3)

In this embodiment, since the water absorption rate S of the partitionwall 4 is set in the adequate range shown in the formula (3), it ispossible to make even an atmosphere in the image display device withoutusing a drying agent.

Hereinafter, as to respective construction members of the image displaypanel according to the invention, particles, liquid powders and commonconstruction members of the first to the sixth aspects of the inventionwill be explained in detail in this order.

At first, the particles used in the first aspect to the sixth aspects ofthe invention will be explained.

The particles may be formed by mixing necessary resin, charge controlagent, coloring agent, additive and so on and grinding them, or, bypolymerizing from monomer, or, by coating a particle with resin, chargecontrol agent, coloring agent, and additive and so on. Hereinafter,typical examples of resin, charge control agent, coloring agent,additive and so on constituting the particles will be explained.

Typical examples of the resin include urethane resin, acrylic resin,polyester resin, acryl urethane resin, silicone resin, nylon resin,epoxy resin, styrene resin, butyral resin, vinylidene chloride resin,melamine resin, phenolic resin, fluorocarbon polymers, and it ispossible to combine two or more resins. For the purpose of controllingthe attaching force with the substrate, polyester resin, acryl urethaneresin, acryl urethane silicone resin, acryl urethane fluoro-carbonpolymers, urethane resin, fluorocarbon polymers are preferred.

Examples of the electric charge control agent include, positive chargecontrol agent including the fourth grade ammonium salt compound,nigrosine dye, triphenylmethane compound, imidazole derivatives, and soon, and negative charge control agent such as metal containing azo dye,salicylic acid metal complex, nitroimidazole derivative and so on.

As for a coloring agent, various kinds of basic or acidic dye may beemployable. Examples include Nigrosine, Methylene Blue, quinolineyellow, rose bengal and do on.

Examples of the inorganic additives include titanium oxide, Chinesewhite, zinc sulfide, antimonial oxide, calcium carbonate, zinc white,talc, silica, calcium silicate, alumina white, cadmium yellow, cadmiumred, cadmium orange, titanium yellow, iron blue, ultramarine blue,cobalt blue, cobalt green, cobalt violet, ferric oxide, carbon black,copper powder, aluminum powder and so on.

Here, in order to further improve a repeating durability, it iseffective to control a stability of the resin constituting theparticles, especially, a water absorbing rate and a solvent insolublerate. It is preferred that the water absorbing rate of the resinconstituting the particles sealed between the substrates is not morethan 3 wt % especially not more than 2 wt %. In this case, a measurementof water absorbing rate is performed according to ASTM-D570 and ameasuring condition is 23° C. for 24 hours.

As for the solvent insoluble rate of the particles, it is preferred thata solvent insoluble rate of the particles, which is defined by thefollowing formula, is not less than 50% more preferably not less than70%:solvent insoluble rate (%)=(B/A)×100;(here, A is a weight of the resin before being immersed into the solventand B is a weight of resin components after the resin is immersed intogood solvent at 25° C. for 24 hours).

If the solvent insoluble rate is less than 50%, a bleed is generated ona surface of the particle when maintaining for a long time. In thiscase, it affects an adhesion power with the particles and prevents amovement of the particles. Therefore, there is a case such that itaffects a durability of the image display.

Here, as a solvent (good solvent) for measuring the solvent insolublerate, it is preferred to use fluoroplastic such as methyl ethyl ketoneand so on, polyamide resin such as methanol and so on, acrylic urethaneresin such as methyl ethyl ketone, toluene and so on, melamine resinsuch as acetone, isopropanol and so on, silicone resin such as tolueneand so on.

Moreover, it is preferred that the particles have a circular shape. Inthe present invention, it is preferred that particle diameterdistribution Span of respective particles, which is defined by thefollowing formula, is not more than 5 preferably not more than 3:Span=(d(0.9)−d(0.1))/d(0.5);(here, d(0.5) means a value of the particle diameter expressed by μmwherein an amount of the particles having the particle diameter largerthan this value is 50% and an amount of the particles having theparticle diameter expressed by μm wherein an amount of the particleshaving a particle diameter smaller than this value is 10%, and d(0.9)means a value of the particle diameter expressed by μm wherein an amountof the particles having the particle diameter smaller than this value is90%). If the particle diameter distribution Span of the particles is setto not more than 5, the particle diameter becomes even and it ispossible to perform an even particle movement.

Further, it is preferred that the average particle diameter d(0.5) ofthe particles is 0.1-50 μm. If the average particle diameter exceedsthis range, a display sharpness is deteriorated, and if the averageparticle diameter is less than this range, a particle movement is notpreferably performed due to an excess agglutination force between theparticles.

Furthermore, as to a relation between the particles, it is important tocontrol a ratio of d(0.5) of the particles having a minimum diameterwith respect to d(0.5) of the particles having a maximum diameter to notlarger than 50 preferably not larger than 10.

If the particle diameter distribution Span is made smaller, theparticles having different charge characteristic with each other aremoved in opposite directions. Therefore, it is preferred that diametersof the particles are substantially same and the same amounts of theparticles are moved in the opposite directions easily, so that thisrange is determined.

Here, the particle diameter distribution and the particle diametermentioned above can be measured by means of a laserdiffraction/scattering method. When a laser light is incident upon theparticles to be measured, a light intensity distribution pattern due toa diffraction/scattering light occurs spatially. This light intensitydistribution pattern corresponds to the particle diameter, and thus itis possible to measure the particle diameter and the particle diameterdistribution. In the present invention, it is defined that the particlediameter and the particle diameter distribution are obtained by a volumestandard distribution. Specifically, the particle diameter and theparticle diameter distribution can be measured by means of a measuringapparatus Mastersizer 2000 (Malvern Instruments Ltd.) wherein theparticles setting in a nitrogen gas flow are calculated by an installedanalysis software (which is based on a volume standard distribution dueto Mie's theory).

Then, the liquid powders used in the first to the sixth aspects of theinvention will be explained.

In the present invention, a term “liquid powder” means an intermediatematerial having both of liquid properties and particle properties andexhibiting a self-fluidity without utilizing gas force and liquid force.Preferably, it is a material having an excellent fluidity such thatthere is no repose angle defining a fluidity of powder. For example, aliquid crystal is defined as an intermediate phase between a liquid anda solid, and has a fluidity showing a liquid characteristic and ananisotropy (optical property) showing a solid characteristic (HeibonshaLtd.: encyclopedia). On the other hand, a definition of the particle isa material having a finite mass if it is vanishingly small and receivesan attraction of gravity (Maruzen Co., Ltd.: physics subject-book).Here, even in the particles, there are special states such as gas-solidfluidized body and liquid-solid fluidized body. If a gas is flown from abottom plate to the particles, an upper force is acted with respect tothe particles in response to a gas speed. In this case, the gas-solidfluidized body means a state that is easily fluidized when the upperforce is balanced with the gravity. In the same manner, the liquid-solidfluidized body means a state that is fluidized by a liquid. (HeibonshaLtd.: encyclopedia) In the present invention, it is found that theintermediate material having both of fluid properties and solidproperties and exhibiting a self-fluidity without utilizing gas forceand liquid force can be produced specifically, and this is defined asthe liquid powder.

That is, as is the same as the definition of the liquid crystal(intermediate phase between a liquid and a solid), the liquid powderaccording to the invention is a material showing the intermediate statehaving both of liquid properties and particle properties, which isextremely difficult to receive an influence of the gravity showing theparticle properties mentioned above and indicates a high fluidity. Sucha material can be obtained in an aerosol state i.e. in a dispersionsystem wherein a solid-like or a liquid-like material is floating in arelatively stable manner as a dispersant in a gas, and thus, in theimage display device according to the invention, a solid material isused as a dispersant.

The image display panel which is a target of the present invention has aconstruction such that the liquid powders composed of a solid materialstably floating as a dispersoid in a gas and exhibiting a high fluidityin an aerosol state are sealed between opposed two substrates, whereinone of two substrates is transparent. Such liquid powders can be made tomove easily and stably by means of Coulomb's force and so on generatedby applying a low voltage.

As mentioned above, the liquid powders means an intermediate materialhaving both of liquid properties and particle properties and exhibitinga self-fluidity without utilizing gas force and liquid force. Suchliquid powders become particularly an aerosol state. In the imagedisplay device according to the invention, the liquid powders used in astate such that a solid material is relatively and stably floating as adispersoid in a gas.

As the aerosol state, it is preferred that an apparent volume in amaximum floating state is two times or more than that in none floatingstate, more preferably 2.5 times or more than that in none floatingstate, and most preferably three times or more than that in nonefloating state. In this case, an upper limit is not defined, but it ispreferred that an apparent volume is 12 times or smaller than that innone floating state.

If the apparent volume in the maximum floating state is smaller than twotimes, a display controlling becomes difficult. On the other hand, ifthe apparent volume in the maximum floating state is larger than 12times, a handling inconvenience during a liquid powder filling operationinto the device such as a particle over-scattering occurs. That is, itis measured by filling the liquid powders in a transparent closed vesselthrough which the liquid powders are seen; vibrating or dropping thevessel itself to obtain a maximum floating state; and measuring anapparent volume at that time from outside of the vessel. Specifically,the liquid powder having a volume ⅕ of the vessel is filled as theliquid powder in a polypropylene vessel with a cap, having a diameter(inner diameter) of 6 cm and a height of 10 cm (product name I-boy®produced by As-one Co., Ltd.), the vessel is set in the vibrator, and avibration wherein a distance of 6 cm is repeated at a speed of 3reciprocating/sec. is performed for 3 hours. Then, the apparent volumein the maximum floating state is obtained from an apparent volume justafter a vibration stop.

Moreover, in the image display panel according to the invention, it ispreferred that a time change of the apparent volume of the liquidpowders satisfies the following formula:V ₁₀ /V ₅>0.8;here, V₅ indicates the apparent volume (cm³) of the liquid powders after5 minutes from the maximum floating state; and V₁₀ indicates theapparent volume (cm³) of the liquid powder after 10 minutes from themaximum floating state. In this case, in the image display panelaccording to the invention, it is preferred to set the time changeV₁₀/V₅ of the apparent volume of the liquid powders to larger than 0.85,more preferably larger than 0.9, most preferably larger than 0.95. Ifthe time change V₁₀/V₅ is not larger than 0.8, the liquid powders aresubstantially equal to normal particles, and thus it is not possible tomaintain a high speed response and durability according to theinvention.

Moreover, it is preferred that the average particle diameter d(0.5) ofthe particle materials constituting the liquid powders is 0.1-20 μm,more preferably 0.5-15 μm, most preferably 0.9-8 μm. If the averageparticle diameter d(0.5) is less than 0.1 μm, a display controllingbecomes difficult. On the other hand, if the average particle diameterd(0.5) is larger than 20 μm, a display is possible, but opacifying poweris decreased and thus a thin shape device is difficult. Here, theaverage particle diameter d(0.5) of the particle materials constitutingthe liquid powder is equal to d(0.5) in the following particle diameterdistribution Span.

It is preferred that particle diameter distribution Span of the particlematerial constituting the liquid powder, which is defined by thefollowing formula, is not more than 5 preferably not more than 3:

Particle diameter distribution: Span=(d(0.9)−d(0.1))/d(0.5); here,d(0.5) means a value of the particle diameter expressed by μm wherein anamount of the particle material constituting the liquid powder havingthe particle diameter larger than this value is 50% and an amount of theparticle material constituting the liquid powder having the particlediameter expressed by μm wherein an amount of the particle materialconstituting the liquid powder having a particle diameter smaller thanthis value is 10%, and d(0.9) means a value of the particle diameterexpressed by μm wherein an amount of the particle material constitutingthe liquid powder having the particle diameter smaller than this valueis 90%. If the particle diameter distribution Span of the particlematerials constituting the liquid powder is set to not more than 5, theparticle diameter becomes even and it is possible to perform an evenliquid powder movement.

Here, the particle diameter distribution and the particle diametermentioned above can be measured by means of a laserdiffraction/scattering method. When a laser light is incident upon theparticles to be measured, a light intensity distribution pattern due toa diffraction/scattering light occurs spatially. This light intensitydistribution pattern corresponds to the particle diameter, and thus itis possible to measure the particle diameter and the particle diameterdistribution. In the present invention, it is defined that the particlediameter and the particle diameter distribution are obtained by a volumestandard distribution. Specifically, the particle diameter and theparticle diameter distribution can be measured by means of a measuringapparatus Mastersizer 2000 (Malvern Instruments Ltd.) wherein theparticles setting in a nitrogen gas flow are calculated by an installedanalysis software (which is based on a volume standard distribution dueto Mie's theory).

The liquid powder may be formed by mixing necessary resin, chargecontrol agent, coloring agent, additive and so on and grinding them, or,by polymerizing from monomer, or, by coating a particle with resin,charge control agent, coloring agent, and additive and so on.Hereinafter, typical examples of resin, charge control agent, coloringagent, additive and so on constituting the liquid powder will beexplained.

Typical examples of the resin include urethane resin, acrylic resin,polyester resin, acryl urethane resin, silicone resin, nylon resin,epoxy resin, styrene resin, butyral resin, vinylidene chloride resin,melamine resin, phenolic resin, fluorocarbon polymers, and it ispossible to combine two or more resins. For the purpose of controllingthe attaching force with the substrate, acryl urethane resin, acrylurethane silicone resin, acryl urethane fluorocarbon polymers, urethaneresin, fluorocarbon polymers are preferred.

Examples of the electric charge control agent include, positive chargecontrol agent including the fourth grade ammonium salt compound,nigrosine dye, triphenylmethane compound, imidazole derivatives, and soon, and negative charge control agent such as metal containing azo dye,salicylic acid metal complex, nitroimidazole derivative and so on.

As for a coloring agent, various kinds of basic or acidic dye may beemployable. Examples include Nigrosine, Methylene Blue, quinolineyellow, rose bengal and do on.

Examples of the inorganic additives include titanium oxide, Chinesewhite, zinc sulfide, antimonial oxide, calcium carbonate, zinc white,talc, silica, calcium silicate, alumina white, cadmium yellow, cadmiumred, cadmium orange, titanium yellow, iron blue, ultramarine blue,cobalt blue, cobalt green, cobalt violet, ferric oxide, carbon black,copper powder, aluminum powder and so on.

However, if the above materials are only mixed or coated with nocontrivance, the liquid powder exhibiting an aerosol state cannot beobtained. The regular method of forming the liquid powder exhibiting anaerosol state is not defined, but the following method is preferablyused.

At first, inorganic fine particles having an average particle size of20-100 nm preferably 20-80 nm are preferably fixed on a surface ofmaterials constituting the liquid powder. Moreover, it is preferred totreat the inorganic fine particles by a silicone oil. Here, as for theinorganic fine particles, use may be made of silicon dioxide (silica),zinc oxide, aluminum oxide, magnesium oxide, cerium oxide, ferric oxide,copper oxide and so on. In this case, a method of fixing the inorganicfine particles is important. For example, use may be made of hybridizer(Nara Machinery Co., Ltd.) or mechano-fusion (Hosokawa Micron Co.,Ltd.), and the liquid powders showing an aerosol state are formed undera predetermined condition (for example processing time).

Here, in order to further improve a repeating durability, it iseffective to control a stability of the resin constituting the liquidpowders, especially, a water absorbing rate and a solvent insolublerate. It is preferred that the water absorbing rate of the resinconstituting the liquid powders sealed between the substrates is notmore than 3 wt % especially not more than 2 wt %. In this case, ameasurement of the water absorbing rate is performed according toASTM-D570 and a measuring condition is 23° C. for 24 hours. As for thesolvent insoluble rate of the resin constituting the liquid powders, itis preferred that a solvent insoluble rate of the liquid powders, whichis defined by the following formula, is not less than 50% morepreferably not less than 70%:solvent insoluble rate (%)=(B/A)×100;(here, A is a weight of the resin before being immersed into the solventand B is a weight after the resin is immersed into good solvent at 25°C. for 24 hours).

If the solvent insoluble rate is less than 50%, a bleed is generated ona surface of the particle material constituting the liquid powders whenmaintaining for a long time. In this case, it affects an adhesion powerwith the liquid powders and prevents a movement of the liquid powders.Therefore, there is a case such that it affects a durability of theimage display. Here, as a solvent (good solvent) for measuring thesolvent insoluble rate, it is preferred to use fluoroplastic such asmethyl ethyl ketone and so on, polyamide resin such as methanol and soon, acrylic urethane resin such as methyl ethyl ketone, toluene and soon, melamine resin such as acetone, isopropanol and so on, siliconeresin such as toluene and so on.

As for a filling amount of the particles or the liquid powders, it ispreferred to control an occupied volume (volume occupied rate) of theparticles or the liquid powders to 3-70 vol %, more preferably 5-60 vol%, most preferably 5-55 vol % of a space between the opposed substrates.If the volume occupied rate of the particles or the liquid powders isless than 3 vol %, a clear image display is not performed, and if itexceeds 70 vol %, the particles or the liquid powders become difficultto move. Here, a space volume means a volume capable of fillingparticles or the liquid powders obtained by substituting an occupiedportion of the partition wall 4 and a seal portion of the device from aspace between the opposed substrates 1 and 2.

Then, the substrate will be explained. At least one of the substrates 1and 2 is the transparent substrate through which a color of theparticles can be observed from outside of the device, and it ispreferred to use a material having a high transmission factor of visiblelight and an excellent heat resistance. Whether a flexibility of thesubstrate is necessary or not is suitably selected in accordance withits use. For example, it is preferred to use a material havingflexibility for the use of electronic paper and so on, and it ispreferred to use a material having no flexibility for the use of adisplay of portable device such as mobile phone, PDA, laptop computerand so on.

Examples of the substrate material include polymer sheets such aspolyethylene terephthalate, polyether sulfone, polyethylene,polycarbonate, polyimide or acryl and inorganic sheets such as glass,quartz or so. The thickness of the substrate is preferably 2 to 5000 μm,more preferably 5 to 1000 μm. When the thickness is too thin, it becomesdifficult to maintain strength and distance uniformity between thesubstrates, and when the thickness is too thick, vividness and contrastas a display capability degrade, and in particular, flexibility in thecase of using for an electronic paper deteriorates.

With respect to the substrate, an electrode may be arranged according toneed. In the case of arranging no electrode on the substrate, theparticles or the liquid powders charged in a predeterminedcharacteristic and having a color is pulled in or rebounds with respectto the substrate by means of an electric field generated by applying anelectrostatic latent image on an outer surface of the substrate. Then,the particles or the liquid powders aligned in accordance with theelectrostatic latent image is observed from outside of the displaydevice through the transparent substrate. In this case, theelectrostatic latent image mentioned above can be generated for exampleby a method wherein an electrostatic latent image generated in a knownelectro-photography system using an electro-photography photo-conductoris transferred and formed on the substrate of the image display deviceaccording to the invention, or, by a method wherein an electrostaticlatent image is directly formed on the substrate by an ion flow.

In the case of arranging an electrode on the substrate, the particles orthe liquid powders charged in a predetermined characteristic and havinga color is pulled in or rebounds with respect to the substrate by meansof an electric field generated on respective electrodes formed on thesubstrate by applying an outer voltage thereto. Then, the particles orthe liquid powders aligned in accordance with the electrostatic latentimage is observed from outside of the display device through thetransparent substrate.

With respect to the electrode arranged to the transparent substrate, theelectrode is formed of electro-conductive materials, which aretransparent and having pattern formation capability. As suchelectro-conductive materials, indium oxide, metals such as aluminum, orconductive polymer such as polyaniline, polypyrrole and polythiopheneformed by vacuum vapor deposition method, coating method, and so on. Itis not necessary to use the transparent electrode arranged on thesubstrate where no transparency is necessary. Additionally, thethickness of the electrode may be suitable unless theelectro-conductivity is absent or any hindrance exists in opticaltransparency, and it is preferable to be 3 to 1000 nm, more preferableto be 5 to 400 nm. In this case, the applied outer voltage may besuperimposed with a direct current or an alternate current. In the casesuch that the electrode is exposed to an outermost surface of thesubstrate, to which the particles or the liquid powders are contacted,it is preferred that the hydrophobic treatment is performed to theelectrode surface together with the substrate surface.

Then, the partition wall will be explained. A shape of the partitionwall is suitably designed in accordance with a size of the particles orthe liquid powders to be used for the display and is not restricted.However, it is preferred to set a width of the partition wall to 2-100μm more preferably 3-50 μm and to set a height of the partition wall to10-5000 μm more preferably 10-500 μm.

Moreover, as a method of forming the partition wall, use may be made ofa double rib method wherein ribs are formed on the opposed substratesrespectively and they are connected with each other and a single ribmethod wherein a rib is formed on one of the opposed substrates only. Inthe image display panel according to the invention, both methods can bepreferably applied.

The display cell formed by the partition walls each made of rib has asquare shape, a triangular shape, a line shape, a circular shape and ahexagon shape, and has an arrangement such as a grid and a honeycomb, asshown in FIG. 10 viewed from a plane surface of the substrate. Theformation method of the partition wall is not particularly restricted,however, a screen-printing method, a sandblast method, aphotolithography method and an additive method. Among them, it ispreferred to use a photolithography method using a resist film.

Then, the first to the sixth aspects of the invention will berespectively explained further specifically with reference to examplesand comparative examples. However, the present invention is not limitedto the examples mentioned below.

(1) Experiments According to the First Aspect of the Invention:

As for the particles, the liquid powders and the display panels obtainedaccording to the examples and the comparative examples, estimations wereperformed in accordance with the standards mentioned below.

(Water Absorption Amount of the Particles)

The water absorption amounts of the particles and the liquid powderswere measured by using Karl Fischer apparatus.

(Estimation of Display Functions)

Black color display and white color display were repeated by inversing apotential of 250V applied to the display device installed in the displaypanel manufactured. The estimation of the display function was performedin such a manner that contrast ratios at initial point, after 10000times repetition, and after 5 days left, were measured by using areflection image densitometer. Here, the contrast ratio was defined bycontrast ratio=reflection density at black display/reflection density ofwhite display. For reference, a maintaining rate was defined as a ratioof the contrast ratio after 10000 times repetition or after 5 days leftwith respect to the initial contrast ratio.

EXAMPLE 1 Particles

The image display panel was manufactured as follows.

At first, a substrate (7 cm×7 cm □) with an electrode was prepared, andon the substrate, a rib having a height of 400 μm was produced to form apartition wall having a stripe shape.

The production of the rib was performed as follows. As an inorganicpowder, a glass powder was prepared by melting, cooling and grinding amixture of SiO₂, Al₂O₃, B₂O₃, Bi₂O₃, and ZnO. As a resin, epoxy resinhaving a heat hardening property was prepared. Then, the glass powderand the epoxy resin were mixed with a solvent and controlled to be aviscosity of 12000 cps, so that a paste was produced. Then, the pastewas applied on the substrate and heated at 150° C. to be hardened. Byrepeating the above paste applying and heating steps, a thickness(corresponding to a height of the partition wall) was controlled to be400 μm. Then, a dry photo-resist was adhered. With respect to theadhered dry photo-resist, an exposing step and an etching step wereperformed so as to form a mask by which a partition wall pattern havinga line of 50 μm, a space of 400 μm and a pitch of 450 μm can be formed.Then, unnecessary portions were removed by a sandblast to form apredetermined partition wall having a stripe shape. In this manner, acell between the partition walls was formed on the substrate.

With respect to the surface of the substrate with the rib, to which theparticles were contacted, OH group adding process was performed by meansof plasma treatment as a pre-treatment, and then 2 g ofhexamethyldisilazan was dropped thereon and it was dried, so that anopposed substrate, to which the surface treatment was performed, wasmanufactured. Moreover, with respect to the one surface of a glasssubstrate, to which indium oxide electrode having a thickness of about500 Å was arranged, OH group adding process was performed by means ofplasma treatment as a pre-treatment, and then 2 g of hexamethyldisilazanwas dropped thereon and it was dried, so that a transparent substrate,to which the surface treatment was performed, was manufactured.

Then, two kinds of the particles (particles A, particles B) wereprepared.

The particles A were produced in such a manner that acrylic urethaneresin: EAU53B (Asia Industry Co., Ltd.)/IPDI cross-linking agent:Excel-Hardener HX (Asia Industry Co., Ltd.), CB (Carbon Black) 4 phr,charge control agent: BontronN07 (Orient Chemical Industries Ltd.) 2 phrwere added, mixed, ground and classified by a jet-mill. The thusproduced particles A were black color particles having a water absorbingrate of 2.9%, a solvent insoluble rate of 91%, an average particlediameter of 9.1 μm and a surface charge density of +25° C./m².

The particles B (white color particles) were produced in such a mannerthat acrylic urethane resin: EAU53B (Asia Industry Co., Ltd.)/IPDIcross-linking agent: Excel-Hardener HX (Asia Industry Co., Ltd.),titanium oxide 10 phr, charge control agent: BontronE89 (Asia IndustryCo., Ltd.) 2 phr were added, mixed, ground and classified by thejet-mill. The thus produced particles B were white color particleshaving a water absorbing rate of 2.9%, a solvent insoluble rate of 91%,an average particle diameter of 7.0 μm and a surface charge density of−60 μC/m².

The particles A were filled in the cells by: moving the substrate withthe rib (opposed substrate), the surface of which was treated byhexamethyldisilazan, in a dried container having a moisture of notgreater than 40% RH; scattering the particles A as first particles inthe container from a nozzle arranged at an upper portion of thecontainer; and filling the scattered particles A in the cells on thesubstrate provided at a lower portion of the container. Continuously,the particles B were filled in the cells on the particles A by:scattering the particles B as second particles in the container from ananother nozzle arranged at an upper portion of the container; andfilling the scattered particles B in the cells, in which the particles Awere previously filled, on the substrate provided at a lower portion ofthe container. The same amounts of the particles A and the particles Bwere mixed with each other, and a total volume occupying rate of theboth particles with respect to a space between two substrates stackedwith a distance was controlled to become 22 vol %.

Then, with respect to the substrate whose cells were filled by theparticles A and the particles B, another substrate (the transparentsubstrate, the surface of which was treated by hexamethyldisilazan) wasstacked. In this case, the peripheral portions of the substrates wereconnected with each other by using an epoxy adhesive and the particleswere sealed therein, so that the display device was manufactured. Afterthat, the estimations of the display function of the thus manufactureddisplay device were performed. The results of the estimations were shownin the following Table 1.

EXAMPLE 2 Liquid Powders

The display panel was manufactured in the same manner as that of theexample 1 except that the liquid powder X and the liquid powder Ymentioned below were used instead of the particles A and the particlesB. The results of the estimations were shown in the following Table 1.

The liquid powders (liquid powder X, liquid powder Y) used here were asfollows.

The liquid powder X was produced as follows. At first, methylmethacrylate monomer, TiO₂ (20 phr), charge control agent Bontron E89(Orient Chemical Industries, Ltd.: 5 phr), initiator AIBN (0.5 phr) weresuspended and polymerized. After that, particle diameters of thepolymerized particles were graded by using a grading device. Then, byusing hybridizer (Nara Machinery Co., Ltd.), the polymerized particles,external additive A (silica H2000, Wacker Ltd.) and external additive B(silica SS20, Japan Silica Ltd.) were set therein and treated at 4800rpm for 5 minuets, so that the external additives were fixed on asurface of the polymerized particles to obtain the liquid powder.

The liquid powder Y was produced as follows. At first, styrene monomer,azo compounds (5 phr), charge control agent Bontron N07 (Orient ChemicalIndustries, Ltd.: 5 phr), initiator AIBN (0.5 phr) were suspended andpolymerized. After that, particle sizes of the polymerized particleswere graded by using a grading device. Then, by using hybridizer (NaraMachinery Co., Ltd.), the polymerized particles, external additive C(silica H2050, Wacker Ltd.) and external additive B (silica SS20, JapanSilica Ltd.) were set therein and treated at 4800 rpm for 5 minuets, sothat the external additives were fixed on a surface of the polymerizedparticles to obtain the liquid powder.

A water content of the particles constituting the liquid powder X was3.0%, a solvent insoluble rate thereof was 92%, an average particlediameter thereof was 3.3 μm, and a surface charge density thereof was+23 μC/m². A water content of the particles constituting the liquidpowder Y was 2.8%, a solvent insoluble rate thereof was 92%, an averageparticle diameter thereof was 3.1 μm, and a surface charge densitythereof was −58 μC/m².

COMPARATIVE EXAMPLE 1 Particles

The display panel was manufactured in the same manner as that of theexample 1 except that the transparent substrate and the opposedsubstrate, to which the surface treatment using hexamethyldisilazan wasperformed, were not used. The results of the estimations were shown inthe following Table 1.

COMPARATIVE EXAMPLE 2 Liquid Powders

The display panel was manufactured in the same manner as that of theexample 2 except that the transparent substrate and the opposedsubstrate, to which the surface treatment using hexamethyldisilazan wasperformed, were not used. The results of the estimations were shown inthe following Table 1. TABLE 1 Comparative Comparative Example 1 Example1 Example 2 Example 2 Hexamethyl- conduct not conduct conduct notconduct disilazan treatment on substrate surface Initial contrast ratio8.2 8.2 8.2 8.2 (a) Contrast ratio after 7.8 6.6 8.0 7.0 10000 timesrepetition (b) Maintaining rate 95 80 98 85 (b)/(a) (%) Contrast ratio7.8 6.2 8.0 6.8 after 5 days left (c) Maintaining rate 95 76 98 83(c)/(a) (%)

From the results shown in Table 1, it is understood that the example 1(particles) and the example 2 (liquid powders), in which the substratesurface is subjected to the hydrophobic treatment usinghexamethyldisilazan, have the same initial contrast ratio but have anexcellent contrast ratio after repetition as compared with thecomparative example 1 (particles) and the comparative example 2 (liquidpowders), in which the substrate surface is not subjected to thehydrophobic treatment using hexamethyldisilazan. From these results, itis understood that the image display panel according to the inventionhas an excellent durability after repetition.

(2) Experiments According to the Second to the Fourth Aspects of theInvention:

As for the image display panel obtained according to the examples andthe comparative examples according to the second to the fourth aspect ofthe invention, estimations were performed in accordance with thestandards mentioned below.

(Universal Hardness)

By using a universal hardness measuring apparatus H100VP-HCUmanufactured by Fischer Instrument Inc., it was measured by the stepsof: preparing a glass substrate having a universal hardness of 2000N/mm²; arranging a measuring specimen made of a material to be measuredand having a thickness of 3 μm on the glass substrate; and performingthe measurement.

(Estimation of Display Function)

The image display panel manufactured by sealing the particles or theliquid powders having different colors and different chargecharacteristics in the cells between the substrates was installed in thedisplay device. The results of the display function was performed insuch a manner that black color display and white color display wererepeated by inversing a potential of 250 V applied to the display deviceand then the display image after the black color display and the whitecolor display were repeated at 100,000 times was enlarged by an opticalmicroscope and was observed by naked eyes.

As to the second aspect of the invention:

EXAMPLE 11 Particles

The image display panel was manufactured as follows.

At first, a substrate (7 cm×7 cm □) with an electrode was prepared, andon the substrate, a rib having a height of 400 μm was produced to form apartition wall having a stripe shape.

The production of the rib was performed as follows. As an inorganicpowder, a glass powder was prepared by melting, cooling and grinding amixture of SiO₂, Al₂O₃, B₂O₃, Bi₂O₃, and ZnO. As a resin, epoxy resinhaving a heat hardening property was prepared. Then, the glass powderand the epoxy resin were mixed with a solvent and controlled to be aviscosity of 12000 cps, so that a paste was produced. Then, the pastewas applied on the substrate and heated at 150° C. to be hardened. Byrepeating the above paste applying and heating steps, a thickness(corresponding to a height of the partition wall) was controlled to be400 μm. Then, a dry photo-resist was adhered. With respect to theadhered dry photo-resist, an exposing step and an etching step wereperformed so as to form a mask by which a partition wall pattern havinga line of 50 μm, a space of 400 μm and a pitch of 450 μm can be formed.Then, unnecessary portions were removed by a sandblast to form apredetermined partition wall having a stripe shape.

With respect to the surface of the partition wall thus manufactured, 2 gof hexamethyldisilazan was dropped and it was dried, so that an opposedsubstrate, in which the surface of the partition wall was treated, wasmanufactured.

Then, two kinds of the particles (particles A, particles B) wereprepared.

The particles A were produced in such a manner that acrylic urethaneresin: EAU53B (Asia Industry Co., Ltd.)/IPDI cross-linking agent:Excel-Hardener HX (Asia Industry Co., Ltd.), CB (Carbon Black) 4 phr,charge control agent: BontronN07 (Orient Chemical Industries Ltd.) 2 phrwere added, mixed, ground and classified by a jet-mill. The thusproduced particles A were black color particles having a water absorbingrate of 2.9%, a solvent insoluble rate of 91%, and an average particlediameter of 9.1 μm.

The particles B were produced in such a manner that acrylic urethaneresin: EAU53B (Asia Industry Co., Ltd.)/IPDI cross-linking agent:Excel-Hardener HX (Asia Industry Co., Ltd.), titanium oxide 10 phr,charge control agent: BontronE89 (Asia Industry Co., Ltd.) 2 phr wereadded, mixed, ground and classified by the jet-mill. The thus producedparticles B were white color particles having a water absorbing rate of2.9%, a solvent insoluble rate of 91%, and an average particle diameterof 7.0 μm.

The particles A were filled in the cells by: moving the substrate withthe rib (opposed substrate), in which the surface of partition wall wastreated by hexamethyldisilazan, in a dried container having a moistureof not greater than 40% RH; scattering the particles A as firstparticles in the container from a nozzle arranged at an upper portion ofthe container; and filling the scattered particles A in the cells on thesubstrate provided at a lower portion of the container. Continuously,the particles B were filled in the cells on the particles A by:scattering the particles B as second particles in the container from ananother nozzle arranged at an upper portion of the container; andfilling the scattered particles B in the cells, in which the particles Awere previously filled, on the substrate provided at a lower portion ofthe container. The same amounts of the particles A and the particles Bwere mixed with each other, and a total volume occupying rate of theboth particles with respect to a space between two substrates stackedwith a distance was controlled to become 22 vol %.

Then, with respect to the substrate whose cells were filled by theparticles, another substrate with no rib (the transparent substrate) wasstacked. In this case, the peripheral portions of the substrates wereconnected with each other by using an epoxy adhesive and the particleswere sealed therein, so that the display device was manufactured. Theresults of the estimations were shown in the following Table 2.

EXAMPLE 12 Liquid Powders

The display panel was manufactured in the same manner as that of theexample 11 except that the liquid powder X and the liquid powder Ymentioned below were used instead of the particles A and the particlesB. The results of the estimations were shown in the following Table 2.

The liquid powders (liquid powder X, liquid powder Y) used here were asfollows.

The liquid powder X was produced as follows. At first, methylmethacrylate monomer, TiO₂ (20 phr), charge control agent Bontron E89(Orient Chemical Industries, Ltd.: 5 phr), initiator AIBN (0.5 phr) weresuspended and polymerized. After that, particle diameters of thepolymerized particles were graded by using a grading device. Then, byusing hybridizer (Nara Machinery Co., Ltd.), the polymerized particles,external additive A (silica H2000, Wacker Ltd.) and external additive B(silica SS20, Japan Silica Ltd.) were set therein and treated at 4800rpm for 5 minuets, so that the external additives were fixed on asurface of the polymerized particles to obtain the liquid powders. Awater content of the particles constituting the liquid powder X was3.0%, a solvent insoluble rate thereof was 92%, and an average particlediameter thereof was 3.3 μm.

The liquid powder Y was produced as follows. At first, styrene monomer,azo compounds (5 phr), charge control agent Bontron N07 (Orient ChemicalIndustries, Ltd.: 5 phr), initiator AIBN (0.5 phr) were suspended andpolymerized. After that, particle sizes of the polymerized particleswere graded by using a grading device. Then, by using hybridizer (NaraMachinery Co., Ltd.), the polymerized particles, external additive C(silica H2050, Wacker Ltd.) and external additive B (silica SS20, JapanSilica Ltd.) were set therein and treated at 4800 rpm for 5 minuets, sothat the external additives were fixed on a surface of the polymerizedparticles to obtain the liquid powder. A water content of the particlesconstituting the liquid powder Y was 2.8%, a solvent insoluble ratethereof was 92%, and an average particle diameter thereof was 3.1 μm.

COMPARATIVE EXAMPLE 11 Particles

The display panel was manufactured in the same manner as that of theexample 11 except that the surface treatment of the partition wall usinghexamethyldisilazan was not performed. The results of the estimationswere shown in the following Table 2.

COMPARATIVE EXAMPLE 12 Liquid Powders

The display panel was manufactured in the same manner as that of theexample 12 except that the surface treatment of the partition wall usinghexamethyldisilazan was not performed. The results of the estimationswere shown in the following Table 2. TABLE 2 Comparative ComparativeExample 11 Example 11 Example 12 Example 12 Particles (or liquid whiteparticles/ white particles/ white liquid white liquid powders) sealedblack particles black particles powder/black powder/black in cell liquidpowder liquid powder Hexamethyldisilazan conduct not conduct conduct notconduct treatment on partition wall surface Display image afterexcellent uneven image excellent uneven image 100,000 times repetition:result of visual observation Display image after not generate generatenot generate generate 100,000 times repetition: particle adhesion topartition wall surface

As to the third aspect of the invention:

EXAMPLE 13 Particles

The display panel was manufactured in the same manner as that of theexample 11 except that the surface treatment of the partition wall usinghexamethyldisilazan was not performed and the surface of the partitionwall was coated by fluorocarbon resin having a small charge decayproperty (LF710N manufactured by ASAHI GLASS CO., LTD.). The results ofthe estimations were shown in the following Table 3.

EXAMPLE 14 Liquid Powders

The display panel was manufactured in the same manner as that of theexample 12 except that the surface treatment of the partition wall usinghexamethyldisilazan was not performed and the surface of the partitionwall was coated by fluorocarbon resin having a small charge decayproperty (LF710N manufactured by ASAHI GLASS CO., LTD.). The results ofthe estimations were shown in the following Table 3.

COMPARATIVE EXAMPLE 13 Particles

The display panel was manufactured in the same manner as that of theexample 13 except that the surface of the partition wall was not coatedby fluorocarbon resin having a small charge decay property (LF710Nmanufactured by ASAHI GLASS CO., LTD.). The results of the estimationswere shown in the following Table 3.

COMPARATIVE EXAMPLE 14 Liquid Powders

The display panel was manufactured in the same manner as that of theexample 14 except that the surface of the partition wall was not coatedby fluorocarbon resin having a small charge decay property (LF710Nmanufactured by ASAHI GLASS CO., LTD.). The results of the estimationswere shown in the following Table 3. TABLE 3 Comparative ComparativeExample 13 Example 13 Example 14 Example 14 Particles (or liquid whiteparticles/ white particles/ white liquid white liquid powders) sealedblack particles black particles powder/black powder/black in cell liquidpowder liquid powder Fluorocarbon resin conduct not conduct conduct notconduct coating (LF710 N) to partition wall surface Display image afterexcellent uneven image excellent uneven image 100,000 times repetition:result of visual observation Display image after not generate generatenot generate generate 100,000 times repetition: particle adhesion topartition wall surface

As to the fourth aspect of the invention:

EXAMPLE 15 Particles

The image display panel was manufactured as follows.

At first, a substrate (7 cm×7 cm □) with an electrode was prepared, andon the substrate, a rib having a height of 400 μm was produced to form apartition wall having a stripe shape.

The production of the rib was performed as follows. As an inorganicpowder, a glass powder was prepared by melting, cooling and grinding amixture of SiO₂, Al₂O₃, B₂O₃, Bi₂O₃, and ZnO. As a resin, epoxy resinhaving a heat hardening property was prepared. Then, the glass powderand the epoxy resin were mixed with a solvent and controlled to be aviscosity of 12000 cps, so that a paste was produced. Then, the pastewas applied on the substrate and heated at 150° C. to be hardened. Byrepeating the above paste applying and heating steps, a thickness(corresponding to a height of the partition wall) was controlled to be400 μm. Then, a dry photo-resist was adhered. With respect to theadhered dry photo-resist, an exposing step and an etching step wereperformed so as to form a mask by which a partition wall pattern havinga line of 50 μm, a space of 400 μm and a pitch of 450 μm can be formed.Then, unnecessary portions were removed by a sandblast to form apredetermined partition wall having a stripe shape.

Then, two kinds of the particles (particles A, particles B) wereprepared in the same manner as that of the example 11, and the imagedisplay panel was manufactured in the same method as that of the example11.

Moreover, only the binder resin used for manufacturing the partitionwall mentioned above (epoxy resin having a thermosetting property) wascoated to the glass substrate having a universal hardness of 2000 N/mm²to be a thickness of 3 μm, and it was heated at 120° C. and washardened, so that a universal hardness of the binder resin (epoxy resinhaving a heat hardening property) was measured. The results of theestimations were shown in the following Table 3.

EXAMPLE 16 Liquid Powders

The partition wall was manufactured in the same manner as that of theexample 15, and the image display panel was manufactured in the samemanner as that of the example 15 except that the two kinds of the liquidpowder X and the liquid powder Y as is the same as the example 12. Theuniversal hardness of the binder resin used for manufacturing thepartition wall (epoxy resin having a thermosetting property) wasmeasured in the same manner as that of the example 15. The results ofthe estimations were shown in the following Table 4.

COMPARATIVE EXAMPLE 15 Particles

The image display panel was manufactured in the same manner as that ofthe example 15 except that a temperature for hardening the binder resinused for the partition wall paste (epoxy resin having a thermosettingproperty) was set to 120° C.

Moreover, only the binder resin used for manufacturing the partitionwall mentioned above (epoxy resin having a thermosetting property) wascoated to the glass substrate having a universal hardness of 2000 N/mm²to be a thickness of 3 μm, and it was heated at 120° C. and washardened, so that a universal hardness of the binder resin (epoxy resinhaving a heat hardening property) was measured. The results of theestimations were shown in the following Table 4.

COMPARATIVE EXAMPLE 16 Liquid Powders

The image display panel was manufactured in the same manner as that ofthe example 16 except that a temperature for hardening the binder resinused for the partition wall paste (epoxy resin having a thermosettingproperty) was set to 120° C. The universal hardness of the binder resinused for manufacturing the partition wall (epoxy resin having athermosetting property) was measured in the same manner as that of thecomparative example 15. The results of the estimations were shown in thefollowing Table 4. TABLE 4 Comparative Comparative Example 15 Example 15Example 16 Example 16 Particles (or liquid white particles/ whiteparticles/ white liquid white liquid powders) sealed black particlesblack particles powder/black powder/black in cell liquid powder liquidpowder Universal hardness 450 −340 450 340 of binder resin for partitionwall (N/mm²) Display image after excellent uneven image excellent unevenimage 100,000 times repetition: result of visual observation Displayimage after not generate generate not generate generate 100,000 timesrepetition: particle adhesion to partition wall surface

From the results of Table 2 to Table 4 mentioned above, it is understoodthat the image display panels according to the second to the fourthaspects of the invention have an excellent durability as compared withthe comparative examples.

(3) Experiment According to the Fifth Aspect of the Invention:

With respect to the thus manufactured image display panels, measurementsand estimations of the functions as the display panel in accordance withthe following standards. The results were shown in the following Table 5and Table 6.

EXAMPLE 21 Particles

The image display panel was manufactured as follows.

At first, a substrate (7 cm×7 cm □) with an electrode was prepared, andon the substrate, a rib having a height of 400 μm was produced to form apartition wall having a stripe shape.

The production of the rib was performed as follows. As an inorganicpowder, a glass powder was prepared by melting, cooling and grinding amixture of SiO₂, Al₂O₃, B₂O₃, Bi₂O₃, and ZnO. As a resin, epoxy resinhaving a heat hardening property was prepared. Then, the glass powderand the epoxy resin were mixed with a solvent and controlled to be aviscosity of 12000 cps, so that a paste was produced. Then, the pastewas applied on the substrate and heated at 150° C. to be hardened. Byrepeating the above paste applying and heating steps, a thickness(corresponding to a height Lh of the partition wall) was controlled tobe 50 μm. Then, a dry photo-resist was adhered. With respect to theadhered dry photo-resist, an exposing step and an etching step wereperformed so as to form a mask by which a partition wall pattern havinga line (corresponding to a width Lw of the partition wall) of 50 μm, aspace of 300 μm and a pitch of 350 μm can be formed. Then, unnecessaryportions were removed by a sandblast to form a predetermined partitionwall having a stripe shape. In this case, a ratio Lh/Lw between theheight and the width of the partition wall 4 was 50/50=1.

Then, two kinds of the particles (particles A, particles B) wereprepared.

The particles A (black color particles) were produced in such a mannerthat acrylic urethane resin: EAU53B (Asia Industry Co., Ltd.)/IPDIcross-linking agent: Excel-Hardener HX (Asia Industry Co., Ltd.), CarbonM100 (manufactured by MITSUBISHI CHEMICAL Co., Ltd.) 4 phr, chargecontrol agent: BontronN07 (Orient Chemical Industries Ltd.) 2 phr wereadded, mixed, ground and classified by a jet-mill.

The particles B (white color particles) were produced in such a mannerthat acrylic urethane resin: EAU53B (Asia Industry Co., Ltd.)/IPDIcross-linking agent: Excel-Hardener HX (Asia Industry Co., Ltd.),titanium oxide 10 phr, charge control agent: BontronE89 (Asia IndustryCo., Ltd.) 2 phr were added, mixed, ground and classified by thejet-mill.

The particles A were filled in the cells by scattering the particles Aas first particles in the container from a nozzle arranged at an upperportion of the container; and filling the scattered particles A in thecells on the substrate provided at a lower portion of the container.Continuously, the particles B were filled in the cells on the particlesA by: scattering the particles B as second particles in the containerfrom an another nozzle arranged at an upper portion of the container;and filling the scattered particles B in the cells, in which theparticles A were previously filled, on the substrate provided at a lowerportion of the container. The same amounts of the particles A and theparticles B were mixed with each other, and a filling rate (total volumeoccupying rate) of the both particles with respect to a space betweentwo glass substrates stacked with a distance was controlled to become 25vol %.

Then, with respect to the substrate 1 whose cells were filled by theparticles A and the particles B, a glass substrate 2 to which indiumoxide electrodes having a thickness of about 500 Å was stacked. In thiscase, the peripheral portions of the substrates were connected with eachother by using an epoxy adhesive and the particles were sealed therein,so that the image display panel was manufactured. Here, as a gas forfilling the gap, use was made of a dried nitrogen gas having a dew pointof −40° C. The thus manufactured image display panel had an openingrate, a white reflectance and a contrast ratio shown in Table 5.

EXAMPLE 22 Particles

The image display panel was manufactured in the same manner as that ofthe above example 21 except that the ratio between the height and thewidth of the partition wall 4 was controlled to be Lh/Lw=50/10=5 bychanging the height Lh of the partition wall 4 to 50 μm and the width Lwof the partition wall 4 to 10 μm. The thus manufactured image displaypanel had an opening rate, a white reflectance and a contrast ratioshown in Table 5.

EXAMPLE 23 Particles

The image display panel was manufactured in the same manner as that ofthe above example 21 except that the ratio between the height and thewidth of the partition wall 4 was controlled to be Lh/Lw=50/5=10 bychanging the height Lh of the partition wall 4 to 50 μm and the width Lwof the partition wall 4 to 5 μm. The thus manufactured image displaypanel had an opening rate, a white reflectance and a contrast ratioshown in Table 5.

EXAMPLE 24 Particles

The image display panel was manufactured in the same manner as that ofthe above example 21 except that the ratio between the height and thewidth of the partition wall 4 was controlled to be Lh/Lw=50/100=0.5 bychanging the height Lh of the partition wall 4 to 50 μm and the width Lwof the partition wall 4 to 100 μm. The thus manufactured image displaypanel had an opening rate, a white reflectance and a contrast ratioshown in Table 5.

EXAMPLE 25 Particles

The image display panel was manufactured in the same manner as that ofthe above example 21 except that the ratio between the height and thewidth of the partition wall 4 was controlled to be Lh/Lw=100/5=20 bychanging the height Lh of the partition wall 4 to 100 μm and the widthLw of the partition wall 4 to 5 μm. The thus manufactured image displaypanel had an opening rate, a white reflectance and a contrast ratioshown in Table 5.

EXAMPLE 26 Liquid Powders

The image display panel was manufactured as follows. At first, asubstrate (7 cm×7 cm □) with an electrode was prepared, and on thesubstrate, a rib having a height of 400 μm was produced to form apartition wall having a stripe shape.

The production of the rib was performed as follows. As an inorganicpowder, a glass powder was prepared by melting, cooling and grinding amixture of SiO₂, Al₂O₃, B₂O₃, Bi₂O₃, and ZnO. As a resin, epoxy resinhaving a heat hardening property was prepared. Then, the glass powderand the epoxy resin were mixed with a solvent and controlled to be aviscosity of 12000 cps, so that a paste was produced. Then, the pastewas applied on the substrate and heated at 150° C. to be hardened. Byrepeating the above paste applying and heating steps, a thickness(corresponding to a height Lh of the partition wall) was controlled tobe 50 μm. Then, a dry photo-resist was adhered. With respect to theadhered dry photo-resist, an exposing step and an etching step wereperformed so as to form a mask by which a partition wall pattern havinga line (corresponding to a width Lw of the partition wall) of 50 μm, aspace of 300 μm and a pitch of 350 μm can be formed. Then, unnecessaryportions were removed by a sandblast to form a predetermined partitionwall having a stripe shape. In this case, a ratio Lh/Lw between theheight and the width of the partition wall 4 was 50/50=1.

Then, two kinds of liquid powders (white liquid powder, black liquidpowder) were prepared.

The white liquid powder (liquid powder X) was produced as follows. Atfirst, methyl methacrylate monomer, TiO₂ (20 phr), charge control agentBontron E89 (Orient Chemical Industries, Ltd.: 5 phr), initiator AIBN(0.5 phr) were suspended and polymerized. After that, particle diametersof the polymerized particles were graded by using a grading device.Then, by using hybridizer (Nara Machinery Co., Ltd.), the polymerizedparticles, external additive A (silica H2000, Wacker Ltd.) and externaladditive B (silica SS20, Japan Silica Ltd.) were set therein and treatedat 4800 rpm for 5 minuets, so that the external additives were fixed ona surface of the polymerized particles to obtain the liquid powder.

The black liquid powder (liquid powder Y) was produced as follows. Atfirst, styrene monomer, azo compounds (5 phr), charge control agentBontron N07 (Orient Chemical Industries, Ltd.: 5 phr), initiator AIBN(0.5 phr) were suspended and polymerized. After that, particle sizes ofthe polymerized particles were graded by using a grading device. Then,by using hybridizer (Nara Machinery Co., Ltd.), the polymerizedparticles, external additive C (silica H2050, Wacker Ltd.) and externaladditive B (silica SS20, Japan Silica Ltd.) were set therein and treatedat 4800 rpm for 5 minuets, so that the external additives were fixed ona surface of the polymerized particles to obtain the liquid powder.

The liquid powder X was filled in the cells by scattering the liquidpowder X as first particles in the container from a nozzle arranged atan upper portion of the container; and filling the scattered liquidpowder X in the cells on the substrate provided at a lower portion ofthe container. Continuously, the liquid powder Y was filled in the cellson the liquid powder X by: scattering the liquid powder Y as secondparticles in the container from an another nozzle arranged at an upperportion of the container; and filling the scattered liquid powder Y inthe cells, in which the liquid powder X was previously filled, on thesubstrate provided at a lower portion of the container. The same amountsof the liquid powder X and the liquid powder Y were mixed with eachother, and a filling rate (total volume occupying rate) of the bothliquid powders with respect to a space between two glass substratesstacked with a distance was controlled to become 25 vol %.

Then, with respect to the substrate 1 whose cells were filled by theliquid powder X and the liquid powder Y, a glass substrate 2 to whichindium oxide electrodes having a thickness of about 500 Å was stacked.In this case, the peripheral portions of the substrates were connectedwith each other by using an epoxy adhesive and the particles were sealedtherein, so that the image display panel was manufactured. Here, as agas for filling the gap, use was made of a dried nitrogen gas having adew point of −40° C. The thus manufactured image display panel had anopening rate, a white reflectance and a contrast ratio shown in Table 6.

EXAMPLE 27 Liquid Powders

The image display panel was manufactured in the same manner as that ofthe above example 26 except that the ratio between the height and thewidth of the partition wall 4 was controlled to be Lh/Lw=50/10=5 bychanging the height Lh of the partition wall 4 to 50 μm and the width Lwof the partition wall 4 to 10 μm. The thus manufactured image displaypanel had an opening rate, a white reflectance and a contrast ratioshown in Table 6.

EXAMPLE 28 Liquid Powders

The image display panel was manufactured in the same manner as that ofthe above example 26 except that the ratio between the height and thewidth of the partition wall 4 was controlled to be Lh/Lw=50/5=10 bychanging the height Lh of the partition wall 4 to 50 μm and the width Lwof the partition wall 4 to 5 μm. The thus manufactured image displaypanel had an opening rate, a white reflectance and a contrast ratioshown in Table 6.

EXAMPLE 29 Liquid Powders

The image display panel was manufactured in the same manner as that ofthe above example 26 except that the ratio between the height and thewidth of the partition wall 4 was controlled to be Lh/Lw=50/100=0.5 bychanging the height Lh of the partition wall 4 to 50 μm and the width Lwof the partition wall 4 to 100 μm. The thus manufactured image displaypanel had an opening rate, a white reflectance and a contrast ratioshown in Table 6.

EXAMPLE 30 Liquid Powders

The image display panel was manufactured in the same manner as that ofthe above example 26 except that the ratio between the height and thewidth of the partition wall 4 was controlled to be Lh/Lw=100/5=20 bychanging the height Lh of the partition wall 4 to 100 μm and the widthLw of the partition wall 4 to 5 μm. The thus manufactured image displaypanel had an opening rate, a white reflectance and a contrast ratioshown in Table 6.

COMPARATIVE EXAMPLE 21 Particles

The image display panel was manufactured in the same manner as that ofthe above example 21 except that the ratio between the height and thewidth of the partition wall 4 was controlled to be Lh/Lw=40/100=0.4 bychanging the height Lh of the partition wall 4 to 40 μm and the width Lwof the partition wall 4 to 100 μm. The thus manufactured image displaypanel had an opening rate, a white reflectance and a contrast ratioshown in Table 5.

COMPARATIVE EXAMPLE 22 Particles

The image display panel was tried to be manufactured in the same manneras that of the above example 21 satisfying a ratio between the heightand the width of the partition wall 4 Lh/Lw=30. However, it was notpossible to manufacture the image display panel since the partition wallhaving extremely slender cross section satisfying the above ratio had abad productivity.

COMPARATIVE EXAMPLE 23 Liquid Powders

The image display panel was manufactured in the same manner as that ofthe above example 26 except that the ratio between the height and thewidth of the partition wall 4 was controlled to be Lh/Lw=40/100=0.4 bychanging the height Lh of the partition wall 4 to 40 μm and the width Lwof the partition wall 4 to 100 μm. The thus manufactured image displaypanel had an opening rate, a white reflectance and a contrast ratioshown in Table 6.

COMPARATIVE EXAMPLE 24 Liquid Powders

The image display panel was tried to be manufactured in the same manneras that of the above example 26 satisfying a ratio between the heightand the width of the partition wall 4 Lh/Lw=30. However, it was notpossible to manufacture the image display panel since the partition wallhaving extremely slender cross section satisfying the above ratio had abad productivity.

If summarized the above results, the opening rates of the image displaypanels according to the example 21 to the example 25 (as is the same asthe example 26 to the example 30), which satisfy the above formula (1)of 0.5≦Lh/Lw≦20, were 73.5, 94.4, 97.2, 51.0 and 98.6 respectively, andthus the desired opening rate could be achieved. On the contrary, theopening rate of the image display panel according to the comparativeexample 21 (as is the same as the comparative example 23) was 41.3, antthus the minimum opening rate required in a practical use was notachieved. Moreover, the image display panel according to the comparativeexample 22 (as is the same as the comparative example 24) was not merelymanufactured.

(Estimation of Display Function)

The estimation of the display function was performed by an image densityof overall white image display (white reflectance: unit %) and acontrast ratio (white reflectance/black reflectance) between an imagedensity of overall white image display (white reflectance: unit %) andan image density of overall black image display (black reflectance: unit%), in the case of white→black or black white overall display image. Asto the measurement of reflectance, use was made of a portable reflectiondensitometer RD19 (manufactured by GretagMacbeth Inc.

(Measurement of Opening Rate)

The width of the partition wall (rib) was measured by means of anoptical microscope, and a calculation was performed on the basis of themeasured result. TABLE 5 Compara- Compara- tive tive Example ExampleExample Example Example Example Example 21 22 23 24 25 21 22 Lh (μm) 5050 50 50 100 40 — Lw (μm) 50 10 5 100 5 100 — Lh/Lw 1 5 10 0.5 20 0.4 —Opening 73.5 94.4 97.2 51.0 98.6 41.3 — rate (%) White 29.4 37.7 38.920.4 42.1 18.3 — reflectance (%) Contrast 9.8 12.6 13.0 6.8 15 4.2 —ratio Remarks not forming rib

TABLE 6 Compara- Compara- tive tive Example Example Example ExampleExample Example Example 26 27 28 29 30 23 24 Lh (μm) 50 50 50 50 100 40— Lw (μm) 50 10 5 100 5 100 — Lh/Lw 1 5 10 0.5 20 0.4 — Opening 73.594.4 97.2 51.0 98.6 41.3 — rate (%) White 29 37.2 38.3 20.1 42.1 18.3 —reflectance (%) Contrast 9.8 12.2 13.0 6.7 15 4.2 — ratio Remarks notforming rib

(4) Experiment According to the Sixth Aspect of the Invention:

With respect to the thus manufactured image display panels, measurementsand estimations of the functions as the display panel in accordance withthe following standards. The results were shown in the following Table 7and Table 8.

EXAMPLE 41 Particles

The image display panel was manufactured as follows.

At first, a substrate (7 cm×7 cm □) with an electrode was prepared, andon the substrate, a rib having a height of 400 μm was produced to form apartition wall having a stripe shape. In this case, as material used forthe partition wall, use was made of a material having a water absorptionrate of 0.1%.

The production of the rib was performed as follows. As an inorganicpowder, a glass powder was prepared by melting, cooling and grinding amixture of SiO₂, Al₂O₃, B₂O₃, Bi₂O₃, and ZnO. As a resin, epoxy resinhaving a heat hardening property was prepared. Then, the glass powderand the epoxy resin were mixed with a solvent and controlled to be aviscosity of 12000 cps, so that a paste was produced. Then, the pastewas applied on the substrate and heated at 150° C. to be hardened. Byrepeating the above paste applying and heating steps, a thickness(corresponding to a height of the partition wall) was controlled to be400 μm. Then, a dry photo-resist was adhered. With respect to theadhered dry photo-resist, an exposing step and an etching step wereperformed so as to form a mask by which a partition wall pattern havinga line of 50 μm, a space of 400 μm and a pitch of 450 μm can be formed.Then, unnecessary portions were removed by a sandblast to form apredetermined partition wall having a stripe shape. In this manner, thecell was formed between the partition walls on the substrates.

Then, two kinds of the particles (particles A, particles B) wereprepared.

The particles A (black color particles) were produced in such a mannerthat acrylic urethane resin: EAU53B (Asia Industry Co., Ltd.)/IPDIcross-linking agent: Excel-Hardener HX (Asia Industry Co., Ltd.), CarbonM100 (manufactured by MITSUBISHI CHEMICAL Co., Ltd.) 4 phr, chargecontrol agent: BontronN07 (Orient Chemical Industries Ltd.) 2 phr wereadded, mixed, ground and classified by a jet-mill.

The particles B (white color particles) were produced in such a mannerthat acrylic urethane resin: EAU53B (Asia Industry Co., Ltd.)/IPDIcross-linking agent: Excel-Hardener HX (Asia Industry Co., Ltd.),titanium oxide 10 phr, charge control agent: BontronE89 (Asia IndustryCo., Ltd.) 2 phr were added, mixed, ground and classified by thejet-mill.

The particles A were filled in the cells by scattering the particles Aas first particles in the container from a nozzle arranged at an upperportion of the container; and filling the scattered particles A in thecells on the substrate provided at a lower portion of the container.Continuously, the particles B were filled in the cells on the particlesA by: scattering the particles B as second particles in the containerfrom an another nozzle arranged at an upper portion of the container;and filling the scattered particles B in the cells, in which theparticles A were previously filled, on the substrate provided at a lowerportion of the container. The same amounts of the particles A and theparticles B were mixed with each other, and a filling rate (total volumeoccupying rate) of the both particles with respect to a space betweentwo glass substrates stacked with a distance was controlled to become 25vol %.

Then, with respect to the substrate 1 whose cells were filled by theparticles A and the particles B, a glass substrate 2 to which indiumoxide electrodes having a thickness of about 500 Å was stacked. In thiscase, the peripheral portions of the substrates were connected with eachother by using an epoxy adhesive and the particles were sealed therein,so that the image display panel was manufactured. Here, as a gas forfilling the gap, use was made of a dried nitrogen gas having a dew pointof −40° C. The thus manufactured image display panel had a waterabsorption rate, an initial contrast ratio and a contrast ratio afterendurance shown in Table 7.

EXAMPLE 42 Particles

The image display panel was manufactured in the same manner as that ofthe example 41 except that use was made of a material having a waterabsorption rate of 5% as a material of the partition wall. The thusmanufactured image display panel had a water absorption rate, an initialcontrast ratio and a contrast ratio after endurance shown in Table 7.

EXAMPLE 43 Particles

The image display panel was manufactured in the same manner as that ofthe example 41 except that use was made of a material having a waterabsorption rate of 10% as a material of the partition wall. The thusmanufactured image display panel had a water absorption rate, an initialcontrast ratio and a contrast ratio after endurance shown in Table 7.

EXAMPLE 44 Liquid Powders

The image display panel was manufactured as follows.

At first, a substrate (7 cm×7 cm □) with an electrode was prepared, andon the substrate, a rib having a height of 400 μm was produced to form apartition wall having a stripe shape. In this case, as material used forthe partition wall, use was made of a material having a water absorptionrate of 0.1%.

The production of the rib was performed as follows. As an inorganicpowder, a glass powder was prepared by melting, cooling and grinding amixture of SiO₂, Al₂O₃, B₂O₃, Bi₂O₃, and ZnO. As a resin, epoxy resinhaving a heat hardening property was prepared. Then, the glass powderand the epoxy resin were mixed with a solvent and controlled to be aviscosity of 12000 cps, so that a paste was produced. Then, the pastewas applied on the substrate and heated at 150° C. to be hardened. Byrepeating the above paste applying and heating steps, a thickness(corresponding to a height of the partition wall) was controlled to be400 μm. Then, a dry photo-resist was adhered. With respect to theadhered dry photo-resist, an exposing step and an etching step wereperformed so as to form a mask by which a partition wall pattern havinga line of 50 μm, a space of 400 μm and a pitch of 450 μm can be formed.Then, unnecessary portions were removed by a sandblast to form apredetermined partition wall having a stripe shape. In this manner, thecell was formed between the partition walls on the substrates.

Then, two kinds of liquid powders (white liquid powder, black liquidpowder) were prepared.

The white liquid powder (liquid powder X) was produced as follows. Atfirst, methyl methacrylate monomer, TiO₂ (20 phr), charge control agentBontron E89 (Orient Chemical Industries, Ltd.: 5 phr), initiator AIBN(0.5 phr) were suspended and polymerized. After that, particle diametersof the polymerized particles were graded by using a grading device.Then, by using hybridizer (Nara Machinery Co., Ltd.), the polymerizedparticles, external additive A (silica H2000, Wacker Ltd.) and externaladditive B (silica SS20, Japan Silica Ltd.) were set therein and treatedat 4800 rpm for 5 minuets, so that the external additives were fixed ona surface of the polymerized particles to obtain the liquid powder.

The black liquid powder (liquid powder Y) was produced as follows. Atfirst, styrene monomer, azo compounds (5 phr), charge control agentBontron N07 (Orient Chemical Industries, Ltd.: 5 phr), initiator AIBN(0.5 phr) were suspended and polymerized. After that, particle sizes ofthe polymerized particles were graded by using a grading device. Then,by using hybridizer (Nara Machinery Co., Ltd.), the polymerizedparticles, external additive C (silica H2050, Wacker Ltd.) and externaladditive B (silica SS20, Japan Silica Ltd.) were set therein and treatedat 4800 rpm for 5 minuets, so that the external additives were fixed ona surface of the polymerized particles to obtain the liquid powder.

The liquid powder X was filled in the cells by scattering the liquidpowder X as first particles in the container from a nozzle arranged atan upper portion of the container; and filling the scattered liquidpowder X in the cells on the substrate provided at a lower portion ofthe container. Continuously, the liquid powder Y was filled in the cellson the liquid powder X by: scattering the liquid powder Y as secondparticles in the container from an another nozzle arranged at an upperportion of the container; and filling the scattered liquid powder Y inthe cells, in which the liquid powder X was previously filled, on thesubstrate provided at a lower portion of the container. The same amountsof the liquid powder X and the liquid powder Y were mixed with eachother, and a filling rate (total volume occupying rate) of the bothliquid powders with respect to a space between two glass substratesstacked with a distance was controlled to become 25 vol %.

Then, with respect to the substrate 1 whose cells were filled by theliquid powder X and the liquid powder Y, a glass substrate 2 to whichindium oxide electrodes having a thickness of about 500 Å was stacked.In this case, the peripheral portions of the substrates were connectedwith each other by using an epoxy adhesive and the particles were sealedtherein, so that the image display panel was manufactured. Since twosubstrates were adhered and sealed in a container in which a driednitrogen gas having a dew point of −40° C. was filled, a gap between thesubstrates in the assembled display panel was filled by a dried nitrogengas (dew point: −40° C.). The thus manufactured image display panel hada water absorption rate, an initial contrast ratio and a contrast ratioafter endurance shown in Table 8.

EXAMPLE 45 Liquid Powders

The image display panel was manufactured in the same manner as that ofthe example 44 except that use was made of a material having a waterabsorption rate of 5% as a material of the partition wall. The thusmanufactured image display panel had a water absorption rate, an initialcontrast ratio and a contrast ratio after endurance shown in Table 8.

EXAMPLE 46 Liquid Powders

The image display panel was manufactured in the same manner as that ofthe example 44 except that use was made of a material having a waterabsorption rate of 10% as a material of the partition wall. The thusmanufactured image display panel had a water absorption rate, an initialcontrast ratio and a contrast ratio after endurance shown in Table 8.

COMPARATIVE EXAMPLE 41 Particles

The image display panel was manufactured in the same manner as that ofthe example 41 except that use was made of a material having a waterabsorption rate of 0.1% as a material of the partition wall. The thusmanufactured image display panel had a water absorption rate, an initialcontrast ratio and a contrast ratio after endurance shown in Table 8,and a display performance was deteriorated after endurance.

COMPARATIVE EXAMPLE 42 Particles

The image display panel was manufactured in the same manner as that ofthe example 41 except that use was made of a material having a waterabsorption rate of 20% as a material of the partition wall. The thusmanufactured image display panel had a water absorption rate, an initialcontrast ratio and a contrast ratio after endurance shown in Table 8,and a display performance was bad initially.

COMPARATIVE EXAMPLE 43 Liquid Powders

The image display panel was manufactured in the same manner as that ofthe example 44 except that use was made of a material having a waterabsorption rate of 0.1% as a material of the partition wall. The thusmanufactured image display panel had a water absorption rate, an initialcontrast ratio and a contrast ratio after endurance shown in Table 8,and a display performance was deteriorated after endurance.

COMPARATIVE EXAMPLE 44 Liquid Powders

The image display panel was manufactured in the same manner as that ofthe example 44 except that use was made of a material having a waterabsorption rate of 20% as a material of the partition wall. The thusmanufactured image display panel had a water absorption rate, an initialcontrast ratio and a contrast ratio after endurance shown in Table 8,and a display performance was bad initially.

If summarized the above results, in the image display panel according tothe example 41 to the example 43 (as is the same as the example 44 tothe example 46) using the partition wall having a water absorption rateS satisfying the above formula (3) of 0.1%≦S≦10%, a variation betweenthe initial contrast ratio and the contrast ratio after endurance wassmall, and a desired display performance could be achieved.

On the contrary, in the image display panel according to the comparativeexample 41 (as is the same as the comparative example 43), a waterabsorption performance of the partition wall was insufficient, and aninversion property became deteriorated due to a water included in thesystem, so that a variation (decrease) between the initial contrastratio and the contrast ratio after endurance was extremely large.Moreover, in the image display panel according to the comparativeexample 42 (as is the same as the comparative example 44), a waterabsorption rate of the partition wall was too high, and a water wasabsorbed excessively during an assemble process, so that undesirableeffects were affected to the display performance initially.

(Estimation of Display Function)

The estimation of the display function was performed by an image densityof overall white image display (white reflectance: unit %) and acontrast ratio (white reflectance/black reflectance) between an imagedensity of overall white image display (white reflectance: unit %) andan image density of overall black image display (black reflectance: unit%), in the case of white black or black→white overall display image. Asto the measurement of reflectance, use was made of a portable reflectiondensitometer RD19 (manufactured by GretagMacbeth Inc.

(Measurement of Water Absorption Rate of Partition Wall)

The water absorption rate of the partition wall was measured inaccordance with ASTM-D570 with respect to the partition wall formed onthe substrate under measuring condition at 23° C. for 24 hours. TABLE 7Example Example Example Comparative Comparative 41 42 43 Example 41Example 42 Water absorption 0.1 5 10 0.05 20 rate (%) Initial contrast10 10 10 10 3 ratio Contrast ratio 9.2 9.5 9.4 6 1 after enduranceRemarks display display performance is performance is deteriorated notgood from after endurance initial state

TABLE 8 Example Example Example Comparative Comparative 44 45 46 Example43 Example 44 Water absorption 0.1 5 10 0.05 20 rate (%) Initialcontrast 10.1 10.1 10.1 10.1 3.2 ratio Contrast ratio 9.3 9.4 9.3 6.21.1 after endurance Remarks display display performance is performanceis deteriorated not good from after endurance initial state

INDUSTRIALLY APPLICABILITY

The image display device according to the invention is applicable to theimage display unit for mobile equipment such as notebook personalcomputers, PDAs, cellular phones and so on; to the electric paper forelectric book, electric newspaper and so on; to the bulletin boards suchas signboards, posters, blackboards and so on; to the image display unitfor electric calculator, home electric application products, autosupplies and so on; to the card display unit for point card, IC card andso on; and to the display unit for electric POP, electric advertisement,electric price tag, electric musical score, RF-ID device and so on.

1. An image display panel: in which at least one group of particles orliquid powders is sealed between opposed substrates, at least one of twosubstrates being transparent; and in which the particles or the liquidpowders, to which an electrostatic field is applied, are made to move soas to display an image; characterized in that use is made of thesubstrate in which at least a surface, to which the particles or theliquid powders are contacted, is subjected to a hydrophobic treatment.2. The image display panel according to claim 1, wherein, as thesubstrate in which the surface, to which the particles or the liquidpowders are contacted, is subjected to the hydrophobic treatment, use ismade of a substrate in which a surface is subjected to ahexamethyldisilazan treatment.
 3. The image display panel according toclaim 2, wherein, prior to the hexamethyldisilazan treatment, OH groupadding process is performed.
 4. The image display panel according toclaim 1, wherein a water absorption rate of the particles or the liquidpowders sealed between the substrates, which is measured according toASTM D570 at 23° C. for 24 hours, is not greater than 3%.
 5. The imagedisplay panel according to claim 1, wherein a volume occupying rate ofthe particles or the liquid powders sealed between the substrates is ina range of 3-70 vol %.
 6. An image display panel: in which one or morethan two cells surrounded by partition walls are formed between opposedtwo substrates with a predetermined distance, at least one of twosubstrates being transparent; in which particles or liquid powders areaccommodated in respective cells; and in which the particles or theliquid powders, to which an electrostatic field is applied, are made tomove so as to display an image; characterized in that at least a surfaceof the partition wall, to which the particles or the liquid powders arecontacted, is subjected to a hydrophobic treatment.
 7. The image displaypanel according to claim 6, wherein the surface of the partition wall,to which the particles or the liquid powders are contacted, is subjectedto the hydrophobic treatment using hexamethyldisilazan.
 8. The imagedisplay panel according to claim 7, wherein, prior to the hydrophobictreatment using hexamethyldisilazan, OH group adding process isperformed.
 9. An image display panel: in which one or more than twocells surrounded by partition walls are formed between opposed twosubstrates with a predetermined distance, at least one of two substratesbeing transparent, to which an electrostatic field is applied, are madeto move so as to display an image; characterized in that at least asurface of the partition wall, to which the particles or the liquidpowders are contacted, is coated by a material having a small chargedecay property.
 10. The image display panel according to claim 9,wherein the material having a small charge decay property is a resinincluding fluorocarbon resin, and, as the fluorocarbon resin, use ismade of one or more than two kinds oftetrafluoroethylene-perfluoroalkylvinylether copolymer,tetrafluoroethylene-hexafluoropropylene-perfluoroalkylvinylether-copolymer,tetrafluoroethylene-ethylene copolymer, polychlorotrifluoroethylene,chlorotrifluoroethylene-ethylene copolymer, polytetrafluoroethylene,polyfluoride and polyvinylfluoride.
 11. The image display panelaccording to claim 9, wherein the material having a small charge decayproperty coated to a surface of the partition wall has such a propertymeasured by a charge decay property measuring method using a coatingmaterial as a film that the maximum surface potential, in the case thatthe surface thereof is charged by a generation of Corona dischargecaused by applying a voltage of 8 KV to a Corona discharge devicedeployed at a distance of 1 mm from the surface, is 300 V or greater at0.3 second after the Corona discharge.
 12. An image display panel: inwhich one or more than two cells surrounded by partition walls areformed between opposed two substrates with a predetermined distance, atleast one of two substrates being transparent; in which particles orliquid powders are accommodated in respective cells; and in which theparticles or the liquid powders, to which an electrostatic field isapplied, are made to move so as to display an image; characterized inthat a universal hardness of a binder resin used for a materialconstituting the partition wall is not less than 400 N/mm², which isobtained by a method of measuring a universal hardness in which thebinder resin constituting the partition wall having a thickness of 3 μmis formed on a glass substrate having a universal hardness of 2000N/mm².
 13. The image display panel according to claim 6, wherein a waterabsorption rate of the particles or the liquid powders sealed betweenthe substrate, which is measured according to ASTM D570 at 23° C. for 24hours, is not greater than 3%.
 14. The image display panel according toclaim 6, wherein a volume occupying rate of the particles or the liquidpowders sealed between the substrates is in a range of 3-70 vol %. 15.The image display panel according to claim 6, wherein: the particles orthe liquid powders to be accommodated in the cell having differentcolors and different charge characteristics and having different chargepotentials; and the particles or the liquid powders, to which anelectrostatic field is applied, are made to move so as to display animage.
 16. An image display panel: in which at least one group ofparticles or liquid powders is sealed respectively in a plurality ofcells formed by partition walls between two substrates, at least one oftwo substrates being transparent; and in which the particles or theliquid powders, to which an electrostatic field is applied, are made tomove so as to display an image; characterized in that a ratio Lh/Lwbetween a height Lh and a width Lw of the partition wall satisfies0.5≦Lh/Lw≦20.
 17. The image display panel according to claim 16, whereinthe ratio Lh/Lw between the height Lh and the width Lw satisfies1≦Lh/Lw≦10.
 18. An image display panel: in which at least one group ofparticles or liquid powders is sealed respectively in a plurality ofcells formed by partition walls between two substrates, at least one oftwo substrates being transparent; and in which the particles or theliquid powders, to which an electrostatic field is applied, are made tomove so as to display an image; characterized in that the partition wallhas a predetermined drying function.
 19. The image display panelaccording to claim 18, wherein a water absorption rate S of thepartition wall satisfies 0.1%≦S≦10%.
 20. An image display devicecharacterized in that the image display panel set forth in claim 1 isinstalled.